Clang added a new feature to the ObjC compiler that will translate method

calls to commonly un-overridden methods into a function that checks whether
the method is overridden anywhere and if not directly dispatches to the
NSObject implementation.

That means if you do override any of these methods, "step-in" will not step
into your code, since we hit the wrapper function, which has no debug info,
and immediately step out again.

Add code to recognize these functions as "trampolines" and a thread plan that
will get us from the function to the user code, if overridden.

<rdar://problem/54404114>

Differential Revision: https://reviews.llvm.org/D73225