flag to disable -Wextra check for unsigned compared to 0

[Ethan Tira-Thompson <ejt@xxxxxxxxxxxxxx>]

Our code has a configuration header file with stuff like:
	const unsigned NUM_SENSORS = N;

Depending on the target we're compiling for, 'N' could be 0.  In  
which case, all our loops:
	for(unsigned i=0; i<NUM_SENSORS; i++) { /* ... */ }
spew the warning:
	warning: comparison of unsigned expression < 0 is always false

I'd like to keep -W / -Wextra enabled for the other things it  
provides, but this particular warning is gumming up the works.

As far as I know, there's no flag (a la -Wno-sign-compare) for this  
particular warning.  Correct?

Can somebody please request (or point me where I can request) a flag  
be added to override this aspect of -Wextra?  From some web  
searching, it appearsmy usage example is a fairly common pattern  
where this warning is discouraging desirable abstraction/generalization.

thanks,
  -ethan