cmake: Use -Werror to make sure we don't get unsupported flags.
cmake: Use -Werror to make sure we don't get unsupported flags.

StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion