In OpenVZ -> CRIU converter I use same build engine
as in criu. But converter has own specifics such as
shipping precompiled vdso.so libraries. So when I
call for "make clean" these precompiled files get
automatically deleted, which in turn cause converter
to fail on next build attempt.

Thus lets delete only *.so targets which are declared
in makefiles.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>