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

[zhijian lin via cfe-commits]

diggerlin wrote:

please do not merge the commit if possible, merging the commit make the review difficult,  We want to compare what change between the two commit when we review. otherwise we have review the patch from scratch.

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