make WITH[OUT]_* more useful?

[Simon J. Gerraty]

On Tue, 1 Apr 2014 19:40:18 +0000, "Bjoern A. Zeeb" writes:
>I am a it worried that we are increasing the number of prefixes again rathe=
>r than reducing it.  I was hoping a while ago that NO_ would die.

NO_ is/was potentially useful.
It allows a makefile to say, "I cannot do that"

Of couse by allowing makefiles to set MK_* directly, they can just 
as easily do MK_*=no
Even then, until you eradicate NO_* it is necessary to handle it?