rootbld: if networking is enabled, copy resolv.conf into the build root

abuild.in

@@ -2139,6 +2139,10 @@ rootbld() {
 	cp /etc/abuild.conf /etc/group /etc/passwd "$BUILD_ROOT/etc"
 	cp /etc/apk/keys/* "$BUILD_ROOT/etc/apk/keys"
 
+	if options_has "net"; then
+		cp /etc/resolv.conf "$BUILD_ROOT/etc"
+	fi
+
 	local version="edge" buildhost="edge" gitref
 	if gitref="$(expr "$(git symbolic-ref --short HEAD)" : '\([0-9]\+\(\.[0-9]\+\)*\)-')"; then
 		version=v${gitref}