[Remarks] Use StringRef::contains to avoid differences in error string

Different OSs have different error strings:

http://lab.llvm.org:8011/builders/clang-ppc64be-linux/builds/39534/steps/ninja%20check%201/logs/FAIL%3A%20LLVM-Unit%3A%3AYAMLRemarks.ParsingBadMeta

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375011 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed