clean_home support

Makefile

+CLEAN_HOME?=/opt/clean
 test: test.icl TTY.icl TTY.dcl Clean\ System\ Files/ctty.o
-	clm -dynamics -l -no-pie -I /opt/clean/lib/Dynamics $(basename $<) -o $@
+	clm -dynamics -l -no-pie -I $(CLEAN_HOME)lib/Dynamics $(basename $<) -o $@
 
 Clean\ System\ Files/ctty.o: tty.c
 	if hash gcc-5 2>/dev/null;\