libdeflate: Avoid circular dependencies

CMake depends on (libdeflate-)gunzip, libdeflate depends on Cmake, so we
can't win.

Luckily libdeflate is _very_ easy to build, without any build system, so
lets just manually compile it and be done with it.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Signed-off-by: Rosen Penev <rosenp@gmail.com>