[clang] [CIR] Upstream func args alloca handling (PR #129167)

[Andy Kaylor via cfe-commits]

================
@@ -52,6 +52,14 @@ class Address {
            elementType);
   }
 
+  Address(mlir::Value pointer, clang::CharUnits alignment)
+      : Address(pointer,
+                mlir::cast<cir::PointerType>(pointer.getType()).getPointee(),
----------------
andykaylor wrote:

The thing that's being cast is `pointer.getType()` and `pointer` is an `mlir::Value` which can basically be any operation that has a pointer type. There is no common base class other than `mlir::Value` that can be used here. 

https://github.com/llvm/llvm-project/pull/129167