pgsql: Unconditionally use the WSA equivalents of Socket error constant

Unconditionally use the WSA equivalents of Socket error constants.

This change will only apply to mingw compilers, and has been found
necessary by late versions of the mingw-w64 compiler. It's the same as
what is done elsewhere for the Microsoft compilers.

Backpatch of commit 73838b5251e.

Problem reported by Michael Cronenworth, although not his patch.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/e536d47ab7eb447ef0be849a8b2e06ae9080017c

Modified Files
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src/include/port/win32.h |   30 ++++++++++--------------------
1 file changed, 10 insertions(+), 20 deletions(-)