[clang] [clang] Add noipa attribute (PR #207502)

[J. Ryan Stinnett via cfe-commits]

jryans wrote:

> Even if we don't have those attributes, if our current noipa implies those behaviors, I think that's still compatible. (which I think LLVM IR noipa /should/ imply those behaviors, but I'm not sure exactly where those things fell in the landing of it)

Yes, although LLVM does not have `noicf` or `noclone` equivalent IR attributes, LLVM’s `noipa` IR attribute already disables the equivalent of GCC’s identical code folding (`MergeFunc` in LLVM) and cloning (`FunctionSpecialization` in LLVM), so it should indeed be compatible.

https://github.com/llvm/llvm-project/pull/207502