Mostly revert 252842 due to failures on some buildbots.

I imagine there's some UB in here somewhere, though Valgrind doesn't
seem to have picked it up (not sure if I have a working asan build right
now to test there).

GDB bot seems to be crashing:
http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/26267/steps/check-all/logs/FAIL%3A%20LLVM%3A%3Adwarfdump-dwp.test

Hexagon ELF bot is, presumably, just getting different output:
http://lab.llvm.org:8011/builders/clang-hexagon-elf/builds/32927/steps/check-all/logs/FAIL%3A%20LLVM%3A%3Adwarfdump-dwp.test

llvm-svn: 252859