compare_tests: Add -compr option

This allows to select how the .sum files are compressed.

It defaults to .xz (what we use in most jobs), but '-compr none'
allows to handle uncompressed sum files, for instance when running
this script right after a GCC build like we do in round-robin jobs.

Change-Id: I5f7085b16a65a470c27ad682be74a6cb8d2e496e
1 file changed