Port header fixes from MSys2

MSys2' Git build script has some changes we should put into Git for
Windows' source code proper.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/mingw.h

@@ -1,14 +1,13 @@
+#include <stdint.h>
+#include <wchar.h>
 #include <winsock2.h>
 #include <ws2tcpip.h>
-
 /*
  * things that are not available in header files
  */
 
-typedef int pid_t;
 typedef int uid_t;
 typedef int socklen_t;
-#define hstrerror strerror
 
 #define S_IFLNK    0120000 /* Symbolic link */
 #define S_ISLNK(x) (((x) & S_IFMT) == S_IFLNK)
@@ -164,8 +163,10 @@ int pipe(int filedes[2]);
 unsigned int sleep (unsigned int seconds);
 int mkstemp(char *template);
 int gettimeofday(struct timeval *tv, void *tz);
+#ifndef __MINGW64_VERSION_MAJOR
 struct tm *gmtime_r(const time_t *timep, struct tm *result);
 struct tm *localtime_r(const time_t *timep, struct tm *result);
+#endif
 int getpagesize(void);	/* defined in MinGW's libgcc.a */
 struct passwd *getpwuid(uid_t uid);
 int setitimer(int type, struct itimerval *in, struct itimerval *out);
@@ -285,8 +286,10 @@ static inline int getrlimit(int resource, struct rlimit *rlp)
 /*
  * Use mingw specific stat()/lstat()/fstat() implementations on Windows.
  */
+#ifndef __MINGW64_VERSION_MAJOR
 #define off_t off64_t
 #define lseek _lseeki64
+#endif
 
 /* use struct stat with 64 bit st_size */
 #ifdef stat