[clang] [clang][PowerPC] Add flag to enable compatibility with GNU for complex arguments (PR #77732)

[Nemanja Ivanovic via cfe-commits]

nemanjai wrote:

My review is not complete, I just submitted what I have so far so at least we can get started on answering the questions I have so far.

https://github.com/llvm/llvm-project/pull/77732