wcsmbs: Improve fortify with clang

It improve fortify checks for wmemcpy, wmemmove, wmemset, wcscpy,
wcpcpy, wcsncpy, wcpncpy, wcscat, wcsncat, wcslcpy, wcslcat, swprintf,
fgetws, fgetws_unlocked, wcrtomb, mbsrtowcs, wcsrtombs, mbsnrtowcs, and
wcsnrtombs.  The compile and runtime checks have similar coverage as
with GCC.

Checked on aarch64, armhf, x86_64, and i686.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>