Configure parallel make recipes

GNU make supports running multiple "jobs" or "recipes" simultaneously,
which should speed up the compilation stage.

See: https://www.gnu.org/software/make/manual/html_node/Parallel.html

builder

@@ -17,7 +17,7 @@ main() {
 			--libexecdir="$prefix/lib" \
 			--enable-multi-arch \
 			--enable-stack-protector=strong
-		make && make install
+		make --jobs=4 && make install
 		tar --dereference --hard-dereference -zcf "/glibc-bin-$version.tar.gz" "$prefix"
 	} >&2