Add platform files for porting to MSVC

Add msvc.c and msvc.h to build git under MSVC.

Signed-off-by: Frank Li <lznuaa@gmail.com>
Signed-off-by: Marius Storm-Olsen <mstormo@gmail.com>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -113,6 +113,9 @@
 /* pull in Windows compatibility stuff */
 #include "compat/mingw.h"
 #endif	/* __MINGW32__ */
+#ifdef _MSC_VER
+#include "compat/msvc.h"
+#endif
 
 #ifndef NO_LIBGEN_H
 #include <libgen.h>