Arrange to supply declarations for strtoll/strtoull if needed.

Buildfarm member dromedary is still unhappy about the recently-added
ecpg "long long" tests.  The reason turns out to be that it includes
"-ansi" in its CFLAGS, and in their infinite wisdom Apple have decided
to hide the declarations of strtoll/strtoull in C89-compliant builds.
(I find it pretty curious that they hide those function declarations
when you can nonetheless declare a "long long" variable, but anyway
that is their behavior, both on dromedary's obsolete macOS version and
the newest and shiniest.)  As a result, gcc assumes these functions
return "int", leading naturally to wrong results.

(Looking at dromedary's past build results, it's evident that this
problem also breaks pg_strtouint64() on 32-bit platforms; but we
evidently have no regression tests that exercise that function with
values above 32 bits.)

To fix, supply declarations for these functions when the platform
provides the functions but not the declarations, using the same type
of mechanism as we use for some other similar cases.

Discussion: https://postgr.es/m/151935568942.1461.14623890240535309745@wrigleys.postgresql.org

configure

@@ -15734,6 +15734,28 @@ _ACEOF
 fi
 done
 
+# strto[u]ll may exist but not be declared
+ac_fn_c_check_decl "$LINENO" "strtoll" "ac_cv_have_decl_strtoll" "$ac_includes_default"
+if test "x$ac_cv_have_decl_strtoll" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_STRTOLL $ac_have_decl
+_ACEOF
+ac_fn_c_check_decl "$LINENO" "strtoull" "ac_cv_have_decl_strtoull" "$ac_includes_default"
+if test "x$ac_cv_have_decl_strtoull" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_STRTOULL $ac_have_decl
+_ACEOF
+
 
 if test "$with_icu" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS

configure.in

@@ -1751,6 +1751,8 @@ fi
 
 AC_CHECK_FUNCS([strtoll strtoq], [break])
 AC_CHECK_FUNCS([strtoull strtouq], [break])
+# strto[u]ll may exist but not be declared
+AC_CHECK_DECLS([strtoll, strtoull])
 
 if test "$with_icu" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS

src/include/c.h

@@ -1096,6 +1096,14 @@ extern int	snprintf(char *str, size_t count, const char *fmt,...) pg_attribute_p
 extern int	vsnprintf(char *str, size_t count, const char *fmt, va_list args);
 #endif
 
+#if defined(HAVE_LONG_LONG_INT) && defined(HAVE_STRTOLL) && !HAVE_DECL_STRTOLL
+extern long long strtoll(const char *str, char **endptr, int base);
+#endif
+
+#if defined(HAVE_LONG_LONG_INT) && defined(HAVE_STRTOULL) && !HAVE_DECL_STRTOULL
+extern unsigned long long strtoull(const char *str, char **endptr, int base);
+#endif
+
 #if !defined(HAVE_MEMMOVE) && !defined(memmove)
 #define memmove(d, s, c)		bcopy(s, d, c)
 #endif

src/include/pg_config.h.in

@@ -170,6 +170,14 @@
    don't. */
 #undef HAVE_DECL_STRNLEN
 
+/* Define to 1 if you have the declaration of `strtoll', and to 0 if you
+   don't. */
+#undef HAVE_DECL_STRTOLL
+
+/* Define to 1 if you have the declaration of `strtoull', and to 0 if you
+   don't. */
+#undef HAVE_DECL_STRTOULL
+
 /* Define to 1 if you have the declaration of `sys_siglist', and to 0 if you
    don't. */
 #undef HAVE_DECL_SYS_SIGLIST

src/include/pg_config.h.win32

@@ -122,6 +122,14 @@
    don't. */
 #define HAVE_DECL_STRNLEN 1
 
+/* Define to 1 if you have the declaration of `strtoll', and to 0 if you
+   don't. */
+#define HAVE_DECL_STRTOLL 1
+
+/* Define to 1 if you have the declaration of `strtoull', and to 0 if you
+   don't. */
+#define HAVE_DECL_STRTOULL 1
+
 /* Define to 1 if you have the declaration of `vsnprintf', and to 0 if you
    don't. */
 #define HAVE_DECL_VSNPRINTF 1