[clang] [AMDGPU] add function attrbute amdgpu-lib-fun (PR #74737)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

Closing this for now. The original backend-libcall consumer, #74741, was closed because its i128 division use case is handled by IR expansion in #80669. I don't have another current use case for the `amdgpu-lib-fun` attribute, so this patch is no longer needed. We can revisit the problem if a concrete consumer appears.


https://github.com/llvm/llvm-project/pull/74737