abuild: add symlinksrc target for create the source file symlinks

needed for upcoming 'rootbld' support

abuild.in

@@ -340,6 +340,18 @@ uri_fetch_mirror() {
 	uri_fetch "$uri"
 }
 
+symlinksrc() {
+	local s
+	mkdir -p "$srcdir"
+	for s in $source; do
+		if is_remote "$s"; then
+			ln -sf "$SRCDEST/$(filename_from_uri $s)" "$srcdir"/
+		else
+			ln -sf "$startdir/$s" "$srcdir/"
+		fi
+	done
+}
+
 default_fetch() {
 	local s
 	mkdir -p "$srcdir"