[NFC] Fix buildbot breaks due to r364375

For some reason, the update_llc_checks.py script produces checks for
empty lines which cause failures. Corrected that to check for actual
text produced by llc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364377 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed