Who maintains dpkg?

That's just bowing to the inevitable: virtually every vendor already has 
such a constant, under some name or other (including GCC). You need it for 
non-confusing overload resolution anyway.

(Plus, to be honest, the overloading of the integer 0 with a specific 
pointer meaning, with the unique stipulation that it need not be 
all-bits-zero, with the corresponding `pointer context' stuff, was a big 
mistake from the start.)