The previous regular expressions were allowing output from
lower log levels. The tests still pass after these changes but will
now catch regressions (previously they would not have).
Other multi-word command line options use hyphens to separate
the words, so the --loglevel option introduced in CMake 3.15 was
inconsistent in this regard. Rename it to --log-level but still support
the original --loglevel name to preserve backward compatibility.