I can't use clang or mingw on windows because it misses certain libraries that I need like winscard and plugin/wav also doesn't compile on either.
However I find applying the workaround* relatively easy and I don't upgrade all that often anyway, so I'll see when it happens and if not, no big deal. Just have to be mindful of that compiler quirk.

* workaround is putting

return String(s);

instead of

return s;

everywhere the warning throws.