pgsql: Fix two places that thought Windows64 is indicated by WIN64 macr

Fix two places that thought Windows64 is indicated by WIN64 macro.

Everyplace else thinks it's _WIN64, so make these places fall in line.

The pg_regress.c usage is not going to result in any change in behavior,
only suppressing (or not) a compiler warning about downcasting HANDLEs.
So there seems no need for back-patching there.

The libpq/win32.mak usage might represent an actual bug, if anyone were
using this script to build for Windows64, which perhaps nobody is.
Given the lack of field complaints, no back-patch here either.

pg_regress.c problem found by Christian Ullrich, the other by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b0e40d189325dc7a54d2546245e766f8c47a7c8d

Modified Files
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src/interfaces/libpq/win32.mak | 2 +-
src/test/regress/pg_regress.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)