Reland "[lldb] Add more ways to find split DWARF files"

This reverts commit dc3f758d.

Lit decided to show me the least interesting part of the
test output, but from what I gather on Mac OS the DWARF
stays in the object files (https://stackoverflow.com/a/12827463).

So either split DWARF options do nothing or they produce
files I don't know the name of that aren't .dwo, so I'm
skipping these tests on Darwin.