[clang] [clang]Implement the c23 stdc bit builtins (PR #185978)

[Timm Baeder via cfe-commits]

tbaederr wrote:

> We'd need to hear from @ldionne or @philnik777 (or others) as to what the STL plans to do here at least for libc++, but it's not uncommon for the C++ standard library to vend a C standard header for use in C++ mode: https://github.com/llvm/llvm-project/blob/main/libcxx/include/stdio.h

https://github.com/llvm/llvm-project/pull/185978