I tried gzip, bzip2, xz and xzstd. Xz 22s for a 128MB disk image. Out of
all other options zstd was both the fastest to compress (<1s) and
produced the smallest file (28MB).

The requirements are checked in mk/depends.mk to be the exact versions
specified here. This way we don't run into version mismatches in CI.

This reverts commit d6fb8b79.