cpp11-migrate: Tweak lit tests to avoid false negatives

Recent failures on a freebsd buildbot indicated a weakness in the
Reformatting.cpp lit test. Tweaking the test to avoid false negatives and
hopefully make the buildbot happy.



git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@187153 91177308-0d34-0410-b5e6-96231b3b80d8