From Jim's post on the lldb-dev mailing list:
This code is there as a backstop for when the unwinder drops a frame at
the beginning of new function/trampoline or whatever.
In the (older_ctx_is_equivalent == false) case we will see if we are at
a trampoline function that somebody knows how to get out of, and
otherwise we will stop.
llvm-svn: 190149