Instead of crashing with a CommandError, now a non-writable location
of mo files will only make compilemessages complain and continue.
Thanks Ramiro Morales for the review.
Fixes#19584.
This implies stop storing file path command line arguments in envvars as
a security measure to start relying on with Popen's shell=False instead,
and addition of an 'utils' module.
Thanks kmichel_wgs for the report.