In some email I received from Chris G. Demetriou, sie wrote:
> 
> > "Chris G. Demetriou" <cgd@pa.dec.com> writes:
> > 
> > > (e.g. people might need to know "bug X in the shared loader was
> > > fixed in -current as of date D, or in bug fix release X.Y.Z")
> > 
> > People should check for features at `configure time'. Hard-coding
> > behaviour based on values of macros is asking for trouble.
> 
> perhaps, but basing behavior on values of macros is what a lot of
> software (including X) wants to do.

Indeed.

Especially as most of the requirements for doing this are so that
things from /usr/include are found properly.

Darren