Add native support for zstd to libarchive

Note that old pkg will failed to build after this. A recent ports tree (one
providing pkg 1.12+) is required to build. Older already built pkg, should
continue working as expected

PR: 238797
Exp run by: antoine
Reviewed by: cem
Approved by: cem
Differential Revision: https://reviews.freebsd.org/D20752