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

[Shilei Tian via llvm-commits]

shiltian wrote:

What is the best case (from the compiler optimization perspective) that we can expect from `amdgpu-max-num-workgroups`? For example, is a smaller value better? I’d imagine that with a smaller value, the compiler can assume each workgroup has access to more resources. If that’s the case, is 1 the best-case scenario? Obviously, 0 doesn’t make much sense.

@jwanggit86 @arsenm 

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