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

[John McCall via llvm-commits]

rjmccall wrote:

Alex, can you talk about why your design decides to check for specific builtins rather than building out the set of features supported by `__builtin_cpu_supports`?

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