squashfs-tools: Add zstd support

This patch adds zstd support to squashfs-tools. It works with zstd
versions >= 1.0.0. It was originally written by Sean Purcell.

Signed-off-by: Sean Purcell <me@seanp.xyz>
Signed-off-by: Nick Terrell <terrelln@fb.com>
5 files changed