Fix ntohl() related warnings about printf formatting

On Windows, ntohl() returns unsinged long.  On Unix it returns
uint32_t.  This makes choosing a suitable printf format string
hard.

This commit introduces a mingw specific helper function
git_ntohl() that casts to unsigned int before returning.  This
makes gcc's printf format check happy.  It should be safe because
we expect ntohl to use 32-bit numbers.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>

git-compat-util.h

@@ -593,6 +593,10 @@ static inline int mingw_fcntl(int fd, int cmd, long arg)
 { return cmd == F_GETFD || cmd == F_SETFD ? 0 : (errno = EINVAL, -1); }
 #define fcntl mingw_fcntl
 
+static inline unsigned int git_ntohl(unsigned int x)
+{ return (unsigned int)ntohl(x); }
+#define ntohl git_ntohl
+
 extern __attribute__((noreturn)) int git_exit(int code);
 #define exit git_exit