Fix LoadableByAddress assert: missing case.
Pattern:
%f = function_ref @invocationClosure : $@convention(thin) (BigStruct) -> ()
%s = struct $InvocationWrapper (%f : $@convention(thin) (BigStruct) -> ())
Error:
Unhandled use of FunctionRefInst
UNREACHABLE executed at /swift/lib/IRGen/LoadableByAddress.cpp:3057!
This fix simply adds the unrecognized case. Rewriting a function_ref
does not change its value, so I'm not sure why the assert exists in
the first place.
