Resubmit "Refactor debuginfo-tests"

This was reverted due to some failures on specific darwin buildbots,
the issue being that the new lit configuration was not setting the
SDKROOT environment variable.  We've tested a fix locally and confirmed
that it works, so this patch resubmits everything with the fix
applied.

llvm-svn: 318435
GitOrigin-RevId: 5e420717a1c4d9b25c645362f92dc02ccf2c5977
4 files changed