WRKSRC. LIBTOOL_OVERRIDE defaults to "libtool */libtool and */*/libtool,"
meaning that, in most packages, there's no need to set it.
So: Nuke tons of LIBTOOL_OVERRIDE=${WRKSRC} and adjust a few
SHLIBTOOL_OVERRIDEs (remove ${WRKSRC} from them).
Add patch-aa, because pkgconfig file was wrong. So bump PKGREVISION too.
Include libXext in buildlink2.mk file and in Makefile.
Add buildlink3.mk file.
