Files compiled with -via-file-asm should be byte for byte identical. This
change improves the checking on dash_s_no_change to detect non-code
differences. If there is a difference, the check goes on to compare code and
debug to try and be more informative.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@238926 91177308-0d34-0410-b5e6-96231b3b80d8