Emit{Nounwind,}RuntimeCall{,OrInvoke} have been modified to take a
FunctionCallee as an argument, and CreateRuntimeFunction has been
modified to return a FunctionCallee. All callers have been updated.
Additionally, CreateBuiltinFunction is removed, as it was redundant
with CreateRuntimeFunction after some previous changes.
This code looks like it implies that the 'if' is never hit? (since cast doesn't propagate null (it asserts/fails/UB on null)) - should this be cast_or_null instead? Or "if(!CGM.getObjCRuntime().getPropertyGetFunction())" ?)
(there are a few similar instances later on)