Clarify comment about gcc -MM.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10875 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

Makefile

@@ -226,7 +226,7 @@ endif
 .depend: $(SRCS) version.h
 	$(CC) -MM $(CFLAGS) $(SDL_CFLAGS) $(filter-out %.h,$^) 1>.depend
 
-# gcc stupidly only outputs the basename of targets
+# gcc stupidly only outputs the basename of targets with -MM
 .vhookdep: $(ALLHOOKS_SRCS)
 	$(CC) $(VHOOKCFLAGS) -MM $^ | sed 's,^\([a-z]\),vhook/\1,' > $@