LibC, LibM: Add functions needed to compile python3

Author: https://github.com/lnzero1dev
Commit: e7affa24dc
Pull-request: https://github.com/SerenityOS/serenity/pull/763
Reviewed-by: https://github.com/awesomekling ✅
Reviewed-by: https://github.com/bugaevc

Libraries/LibC/time.cpp

@@ -134,4 +134,18 @@ int clock_nanosleep(clockid_t clock_id, int flags, const struct timespec* reques
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
+int clock_getres(clockid_t, struct timespec*)
+{
+    ASSERT_NOT_REACHED();
+}
+
+struct tm* gmtime_r(const time_t*, struct tm*)
+{
+    ASSERT_NOT_REACHED();
+}
+
+struct tm* localtime_r(const time_t*, struct tm*)
+{
+    ASSERT_NOT_REACHED();
+}
 }