https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52130
--- Comment #3 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> --- The diagnostic in #1 is not only wrong for this case, it's also a rejects-valid in the case where the underlying types match. I've filed https://gcc.gnu.org/PR81895 for that.
