make: Makefile.build -- Improve autocleanup target

Currently we clean up with wildchar mask. This actually
not that correct. Lets remove only the files were generated
by our make engine.

This as well allows to clean up objects generated as $obj-e
target even if the directory $obj-e is laying in doesn't have
own Makefile.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
libcompel: Build prologue and syscalls

No real use yet, just make lift up and preparations.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>