Makefile: really comment syntax colouring

The unmatched escaped single-quote lies in the middle of a few
function calls, so they too must be fake-closed to properly fix
colour highlighting in some editors.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

Makefile

@@ -1068,7 +1068,7 @@ printvars:
 		$(if $(QUOTED_VARS),\
 			$(info $V='$(subst ','\'',$(if $(RAW_VARS),$(value $V),$($V)))'), \
 			$(info $V=$(if $(RAW_VARS),$(value $V),$($V))))))
-# ' Syntax colouring...
+# ')))) # Syntax colouring...
 
 .PHONY: clean
 clean: