[clang] [llvm] [PowerPC] Add initial support for AMO load builtins (PR #168746)

[Maryam Moghadas via llvm-commits]

maryammo wrote:

> https://lab.llvm.org/buildbot/#/builders/138/builds/22657

The failure is not related to this PR, also the [next build](https://lab.llvm.org/buildbot/#/builders/138/builds/22658) is fine. 

https://github.com/llvm/llvm-project/pull/168746