Use int64_t for timers and mg_millis()

src/arch_win32.h

@@ -89,13 +89,15 @@ typedef int socklen_t;
 
 // https://lgtm.com/rules/2154840805/ -gmtime, localtime, ctime and asctime
 static __inline struct tm *gmtime_r(time_t *t, struct tm *tm) {
-  (void) tm;
-  return gmtime(t);
+  struct tm *x = gmtime(t);
+  *tm = *x;
+  return tm;
 }
 
 static __inline struct tm *localtime_r(time_t *t, struct tm *tm) {
-  (void) tm;
-  return localtime(t);
+  struct tm *x = localtime(t);
+  *tm = *x;
+  return tm;
 }
 
 #endif