[llvm] [clang] [AMDGPU] Adding the amdgpu-num-work-groups function attribute (PR #75647)

[Jun Wang via cfe-commits]

jwanggit86 wrote:

@krzysz00 So, instead of 1 number as in the current implementation, you want 3 numbers, i.e., 3 lines like the following in the metadata section?

```
.num_workgroups_x: 1
.num_workgroups_y: 2
.num_workgroups_z: 3
```

https://github.com/llvm/llvm-project/pull/75647