[clang] [Wunsafe-buffer-usage] Turn off unsafe-buffer warning for methods annotated with clang::unsafe_buffer_usage attribute (PR #125671)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

>rdar://138644831
DO we have to!?!

I don't object to the commit itself once @Fznamznon and @shafik  are happy.

https://github.com/llvm/llvm-project/pull/125671