MSVC: use shipped headers instead of fallback definitions

VS2010 comes with stdint.h [1]
VS2013 comes with inttypes.h [2]

[1] https://stackoverflow.com/a/2628014/3906760
[2] https://blogs.msdn.microsoft.com/vcblog/2013/07/19/c99-library-support-in-visual-studio-2013/

Signed-off-by: Sven Strickroth <sven@cs-ware.de>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Acked-by: Sebastian Schuberth <sschuberth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Sven Strickroth

compat/mingw.h

@@ -406,7 +406,7 @@ static inline void convert_slashes(char *path)
 int mingw_offset_1st_component(const char *path);
 #define offset_1st_component mingw_offset_1st_component
 #define PATH_SEP ';'
-#ifndef __MINGW64_VERSION_MAJOR
+#if !defined(__MINGW64_VERSION_MAJOR) && (!defined(_MSC_VER) || _MSC_VER < 1800)
 #define PRIuMAX "I64u"
 #define PRId64 "I64d"
 #else

compat/vcbuild/include/unistd.h

@@ -45,11 +45,15 @@ typedef unsigned long long uintmax_t;
 
 typedef int64_t off64_t;
 
+#if !defined(_MSC_VER) || _MSC_VER < 1600
 #define INTMAX_MIN  _I64_MIN
 #define INTMAX_MAX  _I64_MAX
 #define UINTMAX_MAX _UI64_MAX
 
 #define UINT32_MAX 0xffffffff  /* 4294967295U */
+#else
+#include <stdint.h>
+#endif
 
 #define STDIN_FILENO  0
 #define STDOUT_FILENO 1