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

[Jun Wang via cfe-commits]

jwanggit86 wrote:

@krzysz00 Code has been updated. Pls take a look when convenient. Pls note the following:
(1) Two attributes are now supported, one for min and one for max num of workgroups.
(2) It is allowed to only specify one of the two attributes.
(3) An attribute is ignored if any one of the 3 numbers (for x,y,z) is 0.
(4) When both attributes are valid, we make sure max >= min element-wise. If not, both are ignored.

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