[libc-commits] [libc] [libc][support][UInt] implement 128b math helpers (PR #86531)

[Nick Desaulniers via libc-commits]

nickdesaulniers wrote:

hmm...I'm on the fence about removing this TODO.

https://github.com/llvm/llvm-project/blob/5ef09540e16dfc81643eaf866d4ada0b52cf27b8/libc/src/__support/CPP/bit.h#L264

On one hand, we now have `__builtin_popcountg` in nascent versions of clang and GCC.  We'd need a `__has_builtin` guard for these.

Actually, I'll add it to this PR.

https://github.com/llvm/llvm-project/pull/86531