xbps-src: support multiple pkg compression formats via etc/conf.

XBPS_PKG_COMPTYPE can be set via etc/conf to set your preferred compression
format; defaults to xz, like xbps-create(1).

The "none" setting is only available since 0.48 (unreleased).

common/hooks/do-pkg/00-gen-pkg.sh

@@ -107,6 +107,7 @@ genpkg() {
 		--source-revisions "${_gitrevs}" \
 		--shlib-provides "${_shprovides}" \
 		--shlib-requires "${_shrequires}" \
+		--compression ${XBPS_PKG_COMPTYPE:=xz} \
 		${_preserve} ${_sourcerevs} ${PKGDESTDIR}
 	rval=$?