Revert "Revert "Remove the darwin gdb option, that version of gdb is now dead and the rest of the compatibility should be done on a dwarf-N level.""

This reverts commit r189913.

Talked with Eric on IRC. I am going to XFAIL the failing test since it
is using what Eric described as "the member hack" which was needed on
that old GDB.

Sorry for the noise!

llvm-svn: 189914