[clang] [CIR] Upstream support for calling through method pointers (PR #176063)

[Henrich Lauko via cfe-commits]

================
@@ -197,6 +224,129 @@ mlir::Operation *LowerItaniumCXXABI::lowerGetRuntimeMember(
                              cir::CastKind::bitcast, memberBytesPtr);
 }
 
+void LowerItaniumCXXABI::lowerGetMethod(
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xlauko wrote:

nit: I believe you can use 
```
ImplicitLocOpBuilder builder(op.getLoc(), rewriter);
```
an then use `builder` instead of explicitly specifing op.getLoc() in every create.

https://github.com/llvm/llvm-project/pull/176063