[llvm] [PowerPC] Support local-dynamic TLS relocation on AIX (PR #66316)

[Felix via llvm-commits]

orcguru wrote:

> Some comments may need follow up, so I posted them first. I will continue to review the code generation part.
> 
> We need a front end patch to eliminate the error report in `clang/lib/Frontend/CompilerInvocation.cpp` and `clang/lib/Sema/SemaDeclAttr.cpp`, right?

I tried to parallelize the review effort, but github didn't show the delta for me: https://github.com/llvm/llvm-project/pull/66972

https://github.com/llvm/llvm-project/pull/66316