Add an -append-exit-code option to bugpoint. This will cause bugpoint to

Add an -append-exit-code option to bugpoint. This will cause bugpoint to
append "exit <retcode>" to the end of the output file. This is used by
the nightly tester to make bugpoint match the output generated by the
RunSafely.sh script so it doesn't find false positives.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31960 91177308-0d34-0410-b5e6-96231b3b80d8