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

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

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/aed8d41af628c2fce661f1156ce4367db41da502

Modified Files
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config/perl.m4 | 30 ++++----
src/tools/msvc/Mkvcbuild.pm | 169 ++++++++++++++++++++++++++++++++++++--------
2 files changed, 158 insertions(+), 41 deletions(-)