Avoid early pipefail exits due to grep failures in stage comparisons.

Avoid early pipefail exits due to grep failures in stage comparisons.

If objects or executables did not contain any RPATH, grep would return
nonzero, and the whole stage comparison loop would unexpectedly exit.
Fix this by checking the grep result explicitly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242722 91177308-0d34-0410-b5e6-96231b3b80d8