Makefile: Correctly clean files in rule (#33)

On systems where GNU Make is present and a different
extension is used at compile time, the clean rule does
not correctly clean out files when requested.

Appending the EXT variable to the list of cleaned files
allows the clean rule to work on this circumstance.

Signed-off-by: Keto <therealketo@gmail.com>

Makefile

@@ -55,6 +55,6 @@ install: all
 	done
 
 clean:
-	rm -rf ldid *.o
+	rm -rf ldid$(EXT) *.o
 
 .PHONY: all clean install