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

[Amy Kwan via cfe-commits]

================
@@ -2540,6 +2540,10 @@ def ffp_contract : Joined<["-"], "ffp-contract=">, Group<f_Group>,
   HelpText<"Form fused FP ops (e.g. FMAs)">,
   Values<"fast,on,off,fast-honor-pragmas">;
 
+def fcomplex_ppc_gnu_abi : Flag<["-"], "fcomplex-ppc-gnu-abi">, Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
+  DocBrief<"Follow the GNU ABI, store Complex values in GPR instead of stack for PowerPC-32">,
----------------
amy-kwan wrote:

```suggestion
  DocBrief<"Follow the GNU ABI, pass Complex values in GPRs instead of the stack for PowerPC-32">,
```

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