Patch remaining undesired usages of MLIR's built-in integer type

[sitio-couto]

There are still some scenarios where we should be using the custom !cir.int type.

Most of these scenarios derive from the CIRGenBuilder.h helper class:

clangir/clang/lib/CIR/CodeGen/CIRGenBuilder.h

Lines 150 to 152 in b24160c

	mlir::Type getInt8Ty() { return typeCache.Int8Ty; }
	mlir::Type getInt32Ty() { return typeCache.Int32Ty; }
	mlir::Type getInt64Ty() { return typeCache.Int64Ty; }

In some cases, the use of built-in integer types makes sense, like in the alignment attribute:

clangir/clang/lib/CIR/CodeGen/CIRGenExpr.cpp

Line 1888 in b24160c

auto alignIntAttr = CGM.getSize(alignment);

In others, like function pointers, we should probably change to cir.int:

clangir/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp

Line 596 in b24160c

auto vtablePtrTy = builder.getVirtualFnPtrType(/*isVarArg=*/true);

[bcardosolopes]

Working on this one right now since it's blocking me!