package/policycoreutils: don't pass DESTDIR when building host variant

package/policycoreutils: don't pass DESTDIR when building host variant

DESTDIR was needed before upstream commit
6b901a4fb80cc61c46f75144b5bb366b8da38e82 ("policycoreutils: build:
follow standard semantics for DESTDIR and PREFIX"), but now the proper
semantic is used for DESTDIR and PREFIX.

However, in addition to the PREFIX that is already passed, we also
need to pass ETCDIR and SBINDIR, which are not defined in terms of
PREFIX.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>