Use appropriate -Wno-warning switches when compiling bitcode.

We use "clang" to compile bitcode files for LLVM inlining.  That might
be different from the build's main C compiler, so it needs its own set
of compiler flags.  To simplify configure, we don't bother adding any
-W switches to that flag set; there's little need since the main build
will show us any warnings.  However, if we don't want to see unwanted
warnings, we still have to add any -Wno-warning switches we'd normally
use with clang.

This escaped notice before commit 9ff47ea41, which tried to add
-Wno-compound-token-split-by-macro; buildfarm animals using mismatched
CC and CLANG still showed those warnings.  I'm not sure why we never
saw any effects from the lack of -Wno-unused-command-line-argument
(maybe that's only activated by -Wall?).  clang does not currently
support -Wno-format-truncation or -Wno-stringop-truncation, although
in the interests of future-proofing and consistency I included tests
for those.

Back-patch to v11 where we started building bitcode files.

Discussion: https://postgr.es/m/2921539.1637254619@sss.pgh.pa.us

configure

@@ -5251,7 +5251,7 @@ else
 fi
 
 # When generating bitcode (for inlining) we always want to use -O2
-# even when --enable-debug is specified. The bitcode it's not going to
+# even when --enable-debug is specified. The bitcode is not going to
 # be used for line-by-line debugging, and JIT inlining doesn't work
 # without at least -O1 (otherwise clang will emit 'noinline'
 # attributes everywhere), which is bad for testing.  Still allow the
@@ -6288,9 +6288,14 @@ if test x"$pgac_cv_prog_CC_cflags__ftree_vectorize" = x"yes"; then
 fi
 
 
-  # We want to suppress clang's unhelpful unused-command-line-argument warnings
-  # but gcc won't complain about unrecognized -Wno-foo switches, so we have to
-  # test for the positive form and if that works, add the negative form
+  #
+  # The following tests want to suppress various unhelpful warnings by adding
+  # -Wno-foo switches.  But gcc won't complain about unrecognized -Wno-foo
+  # switches, so we have to test for the positive form and if that works,
+  # add the negative form.  Note that tests of this form typically need to
+  # be duplicated in the BITCODE_CFLAGS setup stanza below.
+  #
+  # Suppress clang's unhelpful unused-command-line-argument warnings.
   NOT_THE_CFLAGS=""
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS" >&5
 $as_echo_n "checking whether ${CC} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS... " >&6; }
@@ -6335,8 +6340,7 @@ fi
     CFLAGS="$CFLAGS -Wno-unused-command-line-argument"
   fi
   # Remove clang 12+'s compound-token-split-by-macro, as this causes a lot
-  # of warnings when building plperl because of Perl.  Like previously, test
-  # for the positive form and add the negative form
+  # of warnings when building plperl because of usages in the Perl headers.
   NOT_THE_CFLAGS=""
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wcompound-token-split-by-macro, for NOT_THE_CFLAGS" >&5
 $as_echo_n "checking whether ${CC} supports -Wcompound-token-split-by-macro, for NOT_THE_CFLAGS... " >&6; }
@@ -6936,9 +6940,12 @@ fi
 
 
 
-# Determine flags used to emit bitcode for JIT inlining. Need to test
-# for behaviour changing compiler flags, to keep compatibility with
-# compiler used for normal postgres code.
+# Determine flags used to emit bitcode for JIT inlining.
+# 1. We must duplicate any behaviour-changing compiler flags used above,
+# to keep compatibility with the compiler used for normal Postgres code.
+# 2. We don't bother to duplicate extra-warnings switches --- seeing a
+# warning in the main build is enough.
+# 3. But we must duplicate -Wno-warning flags, else we'll see those anyway.
 if test "$with_llvm" = yes ; then
   CLANGXX="$CLANG -xc++"
 
@@ -7206,6 +7213,175 @@ if test x"$pgac_cv_prog_CLANGXX_cxxflags__fexcess_precision_standard" = x"yes";
   BITCODE_CXXFLAGS="${BITCODE_CXXFLAGS} -fexcess-precision=standard"
 fi
 
+
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS" >&5
+$as_echo_n "checking whether ${CLANG} supports -Wunused-command-line-argument, for NOT_THE_CFLAGS... " >&6; }
+if ${pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CLANG}
+CFLAGS="${NOT_THE_CFLAGS} -Wunused-command-line-argument"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument=yes
+else
+  pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument" >&5
+$as_echo "$pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument" >&6; }
+if test x"$pgac_cv_prog_CLANG_cflags__Wunused_command_line_argument" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wunused-command-line-argument"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-unused-command-line-argument"
+  fi
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -Wcompound-token-split-by-macro, for NOT_THE_CFLAGS" >&5
+$as_echo_n "checking whether ${CLANG} supports -Wcompound-token-split-by-macro, for NOT_THE_CFLAGS... " >&6; }
+if ${pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CLANG}
+CFLAGS="${NOT_THE_CFLAGS} -Wcompound-token-split-by-macro"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro=yes
+else
+  pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro" >&5
+$as_echo "$pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro" >&6; }
+if test x"$pgac_cv_prog_CLANG_cflags__Wcompound_token_split_by_macro" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wcompound-token-split-by-macro"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-compound-token-split-by-macro"
+  fi
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -Wformat-truncation, for NOT_THE_CFLAGS" >&5
+$as_echo_n "checking whether ${CLANG} supports -Wformat-truncation, for NOT_THE_CFLAGS... " >&6; }
+if ${pgac_cv_prog_CLANG_cflags__Wformat_truncation+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CLANG}
+CFLAGS="${NOT_THE_CFLAGS} -Wformat-truncation"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_CLANG_cflags__Wformat_truncation=yes
+else
+  pgac_cv_prog_CLANG_cflags__Wformat_truncation=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cflags__Wformat_truncation" >&5
+$as_echo "$pgac_cv_prog_CLANG_cflags__Wformat_truncation" >&6; }
+if test x"$pgac_cv_prog_CLANG_cflags__Wformat_truncation" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wformat-truncation"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-format-truncation"
+  fi
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CLANG} supports -Wstringop-truncation, for NOT_THE_CFLAGS" >&5
+$as_echo_n "checking whether ${CLANG} supports -Wstringop-truncation, for NOT_THE_CFLAGS... " >&6; }
+if ${pgac_cv_prog_CLANG_cflags__Wstringop_truncation+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CLANG}
+CFLAGS="${NOT_THE_CFLAGS} -Wstringop-truncation"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_CLANG_cflags__Wstringop_truncation=yes
+else
+  pgac_cv_prog_CLANG_cflags__Wstringop_truncation=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CLANG_cflags__Wstringop_truncation" >&5
+$as_echo "$pgac_cv_prog_CLANG_cflags__Wstringop_truncation" >&6; }
+if test x"$pgac_cv_prog_CLANG_cflags__Wstringop_truncation" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wstringop-truncation"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-stringop-truncation"
+  fi
 fi
 
 # supply -g if --enable-debug

configure.ac

@@ -440,7 +440,7 @@ else
 fi
 
 # When generating bitcode (for inlining) we always want to use -O2
-# even when --enable-debug is specified. The bitcode it's not going to
+# even when --enable-debug is specified. The bitcode is not going to
 # be used for line-by-line debugging, and JIT inlining doesn't work
 # without at least -O1 (otherwise clang will emit 'noinline'
 # attributes everywhere), which is bad for testing.  Still allow the
@@ -522,17 +522,21 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CC_VAR_OPT(CFLAGS_UNROLL_LOOPS, [-funroll-loops])
   # Optimization flags for specific files that benefit from vectorization
   PGAC_PROG_CC_VAR_OPT(CFLAGS_VECTORIZE, [-ftree-vectorize])
-  # We want to suppress clang's unhelpful unused-command-line-argument warnings
-  # but gcc won't complain about unrecognized -Wno-foo switches, so we have to
-  # test for the positive form and if that works, add the negative form
+  #
+  # The following tests want to suppress various unhelpful warnings by adding
+  # -Wno-foo switches.  But gcc won't complain about unrecognized -Wno-foo
+  # switches, so we have to test for the positive form and if that works,
+  # add the negative form.  Note that tests of this form typically need to
+  # be duplicated in the BITCODE_CFLAGS setup stanza below.
+  #
+  # Suppress clang's unhelpful unused-command-line-argument warnings.
   NOT_THE_CFLAGS=""
   PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wunused-command-line-argument])
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-unused-command-line-argument"
   fi
   # Remove clang 12+'s compound-token-split-by-macro, as this causes a lot
-  # of warnings when building plperl because of Perl.  Like previously, test
-  # for the positive form and add the negative form
+  # of warnings when building plperl because of usages in the Perl headers.
   NOT_THE_CFLAGS=""
   PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wcompound-token-split-by-macro])
   if test -n "$NOT_THE_CFLAGS"; then
@@ -573,9 +577,12 @@ fi
 AC_SUBST(CFLAGS_UNROLL_LOOPS)
 AC_SUBST(CFLAGS_VECTORIZE)
 
-# Determine flags used to emit bitcode for JIT inlining. Need to test
-# for behaviour changing compiler flags, to keep compatibility with
-# compiler used for normal postgres code.
+# Determine flags used to emit bitcode for JIT inlining.
+# 1. We must duplicate any behaviour-changing compiler flags used above,
+# to keep compatibility with the compiler used for normal Postgres code.
+# 2. We don't bother to duplicate extra-warnings switches --- seeing a
+# warning in the main build is enough.
+# 3. But we must duplicate -Wno-warning flags, else we'll see those anyway.
 if test "$with_llvm" = yes ; then
   CLANGXX="$CLANG -xc++"
 
@@ -585,6 +592,27 @@ if test "$with_llvm" = yes ; then
   PGAC_PROG_VARCXX_VARFLAGS_OPT(CLANGXX, BITCODE_CXXFLAGS, [-fwrapv])
   PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, BITCODE_CFLAGS, [-fexcess-precision=standard])
   PGAC_PROG_VARCXX_VARFLAGS_OPT(CLANGXX, BITCODE_CXXFLAGS, [-fexcess-precision=standard])
+
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, NOT_THE_CFLAGS, [-Wunused-command-line-argument])
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-unused-command-line-argument"
+  fi
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, NOT_THE_CFLAGS, [-Wcompound-token-split-by-macro])
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-compound-token-split-by-macro"
+  fi
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, NOT_THE_CFLAGS, [-Wformat-truncation])
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-format-truncation"
+  fi
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_VARCC_VARFLAGS_OPT(CLANG, NOT_THE_CFLAGS, [-Wstringop-truncation])
+  if test -n "$NOT_THE_CFLAGS"; then
+    BITCODE_CFLAGS="$BITCODE_CFLAGS -Wno-stringop-truncation"
+  fi
 fi
 
 # supply -g if --enable-debug