MSVC: Test whether 32-bit Perl needs -D_USE_32BIT_TIME_T.

Commits 5a5c2feca3fd858e70ea348822595547e6fa6c15 and
b5178c5d08ca59e30f9d9428fa6fdb2741794e65 introduced support for modern
MSVC-built, 32-bit Perl, but they broke use of MinGW-built, 32-bit Perl
distributions like Strawberry Perl and modern ActivePerl.  Perl has no
robust means to report whether it expects a -D_USE_32BIT_TIME_T ABI, so
test this.  Back-patch to 9.3 (all supported versions).

The chief alternative was a heuristic of adding -D_USE_32BIT_TIME_T when
$Config{gccversion} is nonempty.  That banks on every gcc-built Perl
using the same ABI.  gcc could change its default ABI the way MSVC once
did, and one could build Perl with gcc and the non-default ABI.

The GNU make build system could benefit from a similar test, without
which it does not support MSVC-built Perl.  For now, just add a comment.
Most users taking the special step of building Perl with MSVC probably
build PostgreSQL with MSVC.

Discussion: https://postgr.es/m/20171130041441.GA3161526@rfd.leadboat.com

1 files changed, 17 insertions, 13 deletions

diff --git a/config/perl.m4 b/config/perl.m4
index 76b1a92e3a..caefb0705e 100644
--- a/config/perl.m4
+++ b/config/perl.m4
@@ -48,19 +48,23 @@ AC_DEFUN([PGAC_CHECK_PERL_CONFIGS],
 
 # PGAC_CHECK_PERL_EMBED_CCFLAGS
 # -----------------------------
-# We selectively extract stuff from $Config{ccflags}.  We don't really need
-# anything except -D switches, and other sorts of compiler switches can
-# actively break things if Perl was compiled with a different compiler.
-# Moreover, although Perl likes to put stuff like -D_LARGEFILE_SOURCE and
-# -D_FILE_OFFSET_BITS=64 here, it would be fatal to try to compile PL/Perl
-# to a different libc ABI than core Postgres uses.  The available information
-# says that all the symbols that affect Perl's own ABI begin with letters,
-# so it should be sufficient to adopt -D switches for symbols not beginning
-# with underscore.  An exception is that we need to let through
-# -D_USE_32BIT_TIME_T if it's present.  (We probably could restrict that to
-# only get through on Windows, but for the moment we let it through always.)
-# For debugging purposes, let's have the configure output report the raw
-# ccflags value as well as the set of flags we chose to adopt.
+# We selectively extract stuff from $Config{ccflags}.  For debugging purposes,
+# let's have the configure output report the raw ccflags value as well as the
+# set of flags we chose to adopt.  We don't really need anything except -D
+# switches, and other sorts of compiler switches can actively break things if
+# Perl was compiled with a different compiler.  Moreover, although Perl likes
+# to put stuff like -D_LARGEFILE_SOURCE and -D_FILE_OFFSET_BITS=64 here, it
+# would be fatal to try to compile PL/Perl to a different libc ABI than core
+# Postgres uses.  The available information says that most symbols that affect
+# Perl's own ABI begin with letters, so it's almost sufficient to adopt -D
+# switches for symbols not beginning with underscore.  Some exceptions are the
+# Windows-specific -D_USE_32BIT_TIME_T and -D__MINGW_USE_VC2005_COMPAT; see
+# Mkvcbuild.pm for details.  We absorb the former when Perl reports it.  Perl
+# never reports the latter, and we don't attempt to deduce when it's needed.
+# Consequently, we don't support using MinGW to link to MSVC-built Perl.  As
+# of 2017, all supported ActivePerl and Strawberry Perl are MinGW-built.  If
+# that changes or an MSVC-built Perl distribution becomes prominent, we can
+# revisit this limitation.
 AC_DEFUN([PGAC_CHECK_PERL_EMBED_CCFLAGS],
 [AC_REQUIRE([PGAC_PATH_PERL])
 AC_MSG_CHECKING([for CFLAGS recommended by Perl])