package/Makefile.in: synchronize pkg-config settings between HOST_{CONFIGURE_OPTS...

package/Makefile.in: synchronize pkg-config settings between HOST_{CONFIGURE_OPTS, MAKE_ENV}

The pkg-config settings in HOST_CONFIGURE_OPTS and HOST_MAKE_ENV have
diverged over time, so they now use different _LIBDIR and
_ALLOW_SYSTEM_{CFLAGS,LIBS} settings.

Conceptually _CONFIGURE_OPTS should be a superset of _MAKE_ENV, so move the
definitions around and define _CONFIGURE_OPTS in terms of _MAKE_ENV instead
of repeating the individual settings.

Do this both for the target and host variant for consistency.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>