Test to check backtraces with machine function splitting.

clang supports option -fsplit-machine-functions and this test checks if the
backtraces are sane when functions are split.

With -fsplit-machine-functions, a function with profiles can get split into 2
parts, the original function containing hot code and a cold part as determined
by the profile info and the cold cutoff threshold.. The cold part gets the
".cold" suffix to disambiguate its symbol from the hot part and can be placed
arbitrarily in the address space.

This test checks if the back-trace looks correct when the cold part is executed.

Differential Revision: https://reviews.llvm.org/D90081