Merge: Makefile: fix make clean

make clean errors out without cleaning everything. Fixes the make file to use rm -f when appropriate and -cmd otherwise.
Added cleaned message at the end to show it completed successfully (otherwise it ends in what can seem like an error message at first glance).
Signed-off-by: Hugo Leblanc <dullin@hololink.org>

Pull-Request: #2730
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>