Disable excessive FP optimization by recent versions of gcc.

Suggested solution from Tom Lane. Problem discovered, probably not
for the first time, while testing the mingw-w64 32 bit compiler.

Backpatched to all live branches.

configure

@@ -4366,6 +4366,67 @@ if test x"$pgac_cv_prog_cc_cflags__fwrapv" = x"yes"; then
   CFLAGS="$CFLAGS -fwrapv"
 fi
 
+  # Disable FP optimizations that cause various errors on gcc 4.5+ or maybe 4.6+
+  { $as_echo "$as_me:$LINENO: checking whether $CC supports -fexcess-precision=standard" >&5
+$as_echo_n "checking whether $CC supports -fexcess-precision=standard... " >&6; }
+if test "${pgac_cv_prog_cc_cflags__fexcess_precision_standard+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -fexcess-precision=standard"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_prog_cc_cflags__fexcess_precision_standard=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_prog_cc_cflags__fexcess_precision_standard=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_prog_cc_cflags__fexcess_precision_standard" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__fexcess_precision_standard" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__fexcess_precision_standard" = x"yes"; then
+  CFLAGS="$CFLAGS -fexcess-precision=standard"
+fi
+
 elif test "$ICC" = yes; then
   # Intel's compiler has a bug/misoptimization in checking for
   # division by NAN (NaN == 0), -mp1 fixes it, so add it to the CFLAGS.

configure.in

@@ -437,6 +437,8 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CC_CFLAGS_OPT([-fno-strict-aliasing])
   # Disable optimizations that assume no overflow; needed for gcc 4.3+
   PGAC_PROG_CC_CFLAGS_OPT([-fwrapv])
+  # Disable FP optimizations that cause various errors on gcc 4.5+ or maybe 4.6+
+  PGAC_PROG_CC_CFLAGS_OPT([-fexcess-precision=standard])
 elif test "$ICC" = yes; then
   # Intel's compiler has a bug/misoptimization in checking for
   # division by NAN (NaN == 0), -mp1 fixes it, so add it to the CFLAGS.