See `python dev/compute_dir_coverage.py -h` for more info

Also, due to some E-ACSL tests depending on glibc (and thus failing on Alpine),
and the fact that E-ACSL does not work on Alpine anyway, the plug-in is now
disabled in that Docker image.

Most plugins do not have a 'headers' directory.
Avoids warnings from frama-c-hdrck when giving such non-existing directories
to the -header-dirs option.

This is less efficient but circumvents a bug in tar --concatenate
(https://superuser.com/questions/941475/concatenate-multiple-tar-files-in-one-command)