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

[zhijian lin via cfe-commits]

diggerlin wrote:

I do not further comment on the PR, 

but I have worry about that , the PR have different mechanism with "-msoft-float" , the -msoft-float pass "use-soft-float"="true" in the IR, the llc will l put float parameter in the GPR, but the PR implement `-fcomplex-ppc-gnu-abi` in the frontend  , can we implement  `-fcomplex-ppc-gnu-abi`  as  "-msoft-float"   ?

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