[libc] Implement wctype header

[mleleszi]

Tracking issue for the UTF8 wctype implementation based on https://discourse.llvm.org/t/rfc-libc-wctype-header-implementation/88941/10

@michaelrj-google @bassiounix

[llvmbot]

@llvm/issue-subscribers-libc

Author: Marcell Leleszi (mleleszi)

Tracking issue for the UTF8 wctype implementation based on https://discourse.llvm.org/t/rfc-libc-wctype-header-implementation/88941/10

@michaelrj-google @bassiounix