[clang] [llvm] [AMDGPU] Adding the amdgpu-num-work-groups function attribute (PR #79035)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Clang changes look fine, but I don't have the expertise to review the LLVM changes, so whoever reviews LLVM feel free to 'approve' when you're ready.

https://github.com/llvm/llvm-project/pull/79035