[clang] [PowerPC] make `_Complex` ABI GCC-compatible (PR #208917)

[Folkert de Vries via cfe-commits]

folkertdev wrote:

Ping for the IBM folks @amy-kwan @daltenty @lei137.

The ABI is clearly broken, people have been running into this for years. Seems like something you'd want to see fixed.

I've updated the references from LLVM 22 -> 23.

https://github.com/llvm/llvm-project/pull/208917