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

[zhijian lin via cfe-commits]

================
@@ -330,22 +330,33 @@ namespace {
 class PPC32_SVR4_ABIInfo : public DefaultABIInfo {
   bool IsSoftFloatABI;
   bool IsRetSmallStructInRegABI;
+  bool IsComplexInRegABI;
----------------
diggerlin wrote:

do we need a new data member `IsComplexInRegABI` here ? (there are several place code be modified because we add the new data member `IsComplexInRegABI` )

we can add 

```
bool IsComplexInRegABI = getCodeGenOpts().getComplexInRegABI() ==
                            CodeGenOptions::CMPLX_InGPR ;
```
                            
in the function  `classifyArgumentType` and `classifyReturnType()`

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