[PATCH] Fix double-inclusion of pg_config_os.h when building extensions with Visual Studio

Hi all

Related to the earlier comments about building extensions on Windows, I
just noticed that we don't treat "WINDLL" as equivalent to "WIN32", and
"WIN32" isn't set in a Visual Studio DLL project.

We should actually be testing _WIN32, which is the compiler's
pre-defined macro. The attached patch to c.h takes care of that - it
tests _WIN32 in c.h and sets WIN32 early if it's found.

_WIN32 is set for both win32 and win64, like we expect from WIN32.

Without this patch, MSVC extension builds fail with:

9.3\include\server\pg_config_os.h(207): error C2011: 'timezone' :
'struct' type redefinition
1> c:\program
files\postgresql\9.3\include\server\pg_config_os.h(207) : see
declaration of 'timezone'
1>c:\program files\postgresql\9.3\include\server\pg_config_os.h(216):
error C2011: 'itimerval' : 'struct' type redefinition
1> c:\program
files\postgresql\9.3\include\server\pg_config_os.h(216) : see
declaration of 'itimerval'

due to double-inclusion of pg_config_os.h from c.h:57 then later on
c.h:92 . WIN32 is not defined on line 57 (so we include pg_config_os.h),
but gets defined by the include of crtdefs.h so we re-include it again
later.

This doesn't cause issues with our Perl build system because we set WIN32.

--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services