[clang] [llvm] AMDGPU: Move attributor into optimization pipeline (PR #83131)

[via cfe-commits]

dyung wrote:

@arsenm are you aware that there is a test failure from this change that is still failing now about 16 hours later? Can you please take a look and revert if you need time to investigate so that we can get the bots back to green?

Some failing bots:
1. https://lab.llvm.org/buildbot/#/builders/144/builds/2221
2. https://lab.llvm.org/buildbot/#/builders/46/builds/1587
3. https://lab.llvm.org/buildbot/#/builders/190/builds/1798

https://github.com/llvm/llvm-project/pull/83131