[clang] [llvm] [SPIRV][AMDGPU][clang][CodeGen][opt] Add late-resolved feature identifying predicates (PR #134016)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

It's been awhile since I've looked at this. From what I understand, what we want is basically a `__builtin_cpu_supports` that's resolved by the backend rather than runtime. That's presumably just checking the feature set of the target, either through the function's attributes or default set. Is what we're doing here fundamentally different?

https://github.com/llvm/llvm-project/pull/134016