api: Fix api.so and libgfapi.so build time dependency

Not all versions of autoconf handle dependencies expressed
as "A: B". Use the xxx_DEPENDENCIES variable to make it
version independent

Change-Id: Ia0b13399d0bf10995d9845e04cd9eb3ef6518dbe
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5118
Reviewed-by: Raghavendra Talur <rtalur@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>