build: fix fallout from swithing to common shared lib

build: fix fallout from swithing to common shared lib

when building corosync on a clean system or for the very first
time, corosync_common needs to be visible both via -L for link
and for the LD_PATH, otherwise the linker cannot resolve
normal library dependencies.

This issue does NOT affect corosync users, but it's confined
to internal corosync only.

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>