This requires moving test files so that the Makefile for the tests can be
included after building libstrongswan, which requires the plugin when
building monolithically. Due to this a static helper library is required
as directly referring to object files (or source files) is not possible.
It's also necessary to avoid any link-time dependency on libstrongswan in
bliss_huffman, to avoid circular dependencies (bliss_huffman -> libstrongswan
-> bliss -> bliss_huffman).