[clang] [CIR] Better handling of `void` function return (PR #128089)

[Henrich Lauko via cfe-commits]

================
@@ -375,11 +410,48 @@ void printFuncTypeArgs(mlir::AsmPrinter &p, mlir::ArrayRef<mlir::Type> params,
   p << ')';
 }
 
+// Use a custom parser to handle the optional return and argument types without
+// an optional anchor.
+static mlir::ParseResult parseFuncType(mlir::AsmParser &p,
+                                       mlir::Type &optionalReturnTypes,
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xlauko wrote:

```suggestion
                                       mlir::Type &optionalReturnType,
```

https://github.com/llvm/llvm-project/pull/128089