Makefile: clean up cppcheck.txt

Makefile

@@ -12,6 +12,7 @@ TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs \
 				multibrot-openmp hello-openmp mandelbrot-openmp
 EXTRAS=mandelbrot.bmp multibrot.png test-inline-assembly.s tags \
 			 mtrace-test.trace mtrace-test.txt multibrot-openmp.png
+VERYEXTRAS=cppcheck.txt
 
 .PHONY: all
 all: $(TARGETS)
@@ -21,7 +22,7 @@ really-all: all $(EXTRAS)
 
 .PHONY: clean
 clean:
-	rm -f $(TARGETS) $(EXTRAS) *.o *~ cppcheck.txt
+	rm -f $(TARGETS) $(EXTRAS) $(VERYEXTRAS) *.o *~
 
 .PHONY: cppcheck
 cppcheck: cppcheck.txt