Preserve --compile-no-warning-as-error in automatic CMake re-runs

When the build system re-runs cmake to regenerate itself, preserve the --compile-no-warning-as-error option if it was used when cmake was last explicitly invoked. Normally such settings are preserved in the cache, but the purpose of this option is to be beyond the reach of project code.

This is a follow-up fix to !7268 (merged).