xbps-src: use "virtual?" keyword to declare virtual runtime dependencies.

The syntax "pkg?vpkg" can be used in hostmakedepends, makedepends and depends;
but the "virtual" keyword can be declared specifically for runtime dependencies
(depends).

common/hooks/post-install/04-generate-runtime-deps.sh

@@ -156,6 +156,7 @@ hook() {
 
 	if [ -n "$run_depends" ]; then
 		echo "$run_depends" > ${PKGDESTDIR}/rdeps
+		sed 's,virtual?,,g' -i ${PKGDESTDIR}/rdeps
 	fi
 	if [ -n "${sorequires}" ]; then
 		echo "${sorequires}" > ${PKGDESTDIR}/shlib-requires