Windows: do not redefine _WIN32_WINNT

With MinGW runtime version 4.0 this interferes with the previous
definition from sdkddkver.h.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/nedmalloc/malloc.c.h

@@ -499,7 +499,9 @@ MAX_RELEASE_CHECK_RATE   default: 4095 unless not HAVE_MMAP
 #endif  /* WIN32 */
 #ifdef WIN32
 #define WIN32_LEAN_AND_MEAN
+#ifndef _WIN32_WINNT
 #define _WIN32_WINNT 0x403
+#endif
 #include <windows.h>
 #define HAVE_MMAP 1
 #define HAVE_MORECORE 0

compat/poll/poll.c

@@ -39,7 +39,7 @@
 
 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
 # define WIN32_NATIVE
-# if defined (_MSC_VER)
+# if defined (_MSC_VER) && !defined(_WIN32_WINNT)
 #  define _WIN32_WINNT 0x0502
 # endif
 # include <winsock2.h>

git-compat-util.h

@@ -86,7 +86,7 @@
 #define _SGI_SOURCE 1
 
 #if defined(WIN32) && !defined(__CYGWIN__) /* Both MinGW and MSVC */
-# if defined (_MSC_VER)
+# if defined (_MSC_VER) && !defined(_WIN32_WINNT)
 #  define _WIN32_WINNT 0x0502
 # endif
 #define WIN32_LEAN_AND_MEAN  /* stops windows.h including winsock.h */