use SDL's functions version inplace of libc version

src/locale/SDL_locale.c

@@ -45,7 +45,7 @@ build_locales_from_csv_string(char *csv)
 
     num_locales++;  /* one more for terminator */
 
-    slen = ((size_t) (ptr - csv)) + 1;  /* strlen(csv) + 1 */
+    slen = ((size_t) (ptr - csv)) + 1;  /* SDL_strlen(csv) + 1 */
     alloclen = slen + (num_locales * sizeof (SDL_Locale));
 
     loc = retval = (SDL_Locale *) SDL_calloc(1, alloclen);