dir-locals.el: Set indent-tabs-mode true for makefile-mode

Makefiles need hard tabs, let's not make that harder than it needs to be.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>

.dir-locals.el

@@ -8,4 +8,5 @@
 	    (c-set-offset 'innamespace '0)
 	    (c-set-offset 'inline-open '0)))
   )
+ (makefile-mode (indent-tabs-mode . t))
  )