LibC: Stub out wcsftime()

Author: https://github.com/alimpfard
Commit: 687a3351c2
Pull-request: https://github.com/SerenityOS/serenity/pull/11324
Reviewed-by: https://github.com/BertalanD

Userland/Libraries/LibC/wchar.h

@@ -95,4 +95,6 @@ int vfwscanf(FILE* __restrict stream, const wchar_t* __restrict format, va_list
 int vswscanf(const wchar_t* __restrict ws, const wchar_t* __restrict format, va_list arg);
 int vwscanf(const wchar_t* __restrict format, va_list arg);
 
+size_t wcsftime(wchar_t* __restrict wcs, size_t maxsize, const wchar_t* __restrict format, const struct tm* __restrict timeptr);
+
 __END_DECLS