Fork project on github will cause submodule trying to
fetch submodule under fork user not cloudius-system.

Signed-off-by: Yang Bai <hamo.by@gmail.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

Used for zlib and similar minor libraries.

Style requires manual edititing of loader.cc to run, no automated way
to pick up whole directories in the manifest, and we won't clear the
environment before running the next .so

Suggested by Christoph.