BUILDLINK_PREFIX.<pkgname>. This allows buildlink to find X11BASE packages
regardless of whether they were installed before or after xpkgwedge was
installed. Idea by Alistair Crooks <agc@pkgsrc.org>.
pilot-link-libs depend on this most recent version (0.9.5). Conveniently,
all the packages using buildlink.mk files have dependencies automatically
updated by modifying this one location.