w64: Add definition of FMT_pid

For mingw-w64, pid_t is _pid_t which is __int64,
so this platform needs its own definition of FMT_pid.
Reviewed-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

osdep.h

@@ -130,6 +130,8 @@ int qemu_madvise(void *addr, size_t len, int advice);
 
 #if defined(__HAIKU__) && defined(__i386__)
 #define FMT_pid "%ld"
+#elif defined(WIN64)
+#define FMT_pid "%" PRId64
 #else
 #define FMT_pid "%d"
 #endif