tiny winsup config patch

[DJ Delorie]

> Why would we use the installed cross-compiler's headers?

Because gcc may pick up <stdio.h> there by default when we build, say,
mount.exe

> If someone has winsup installed without newlib then this will just
> work.

If someone has winsup installed without newlib, they can't build
cygwin1.dll - can they?

> If they don't then they should keep everything up to date.
> ../newlib/lib[cm].a should be up to date with respect to the
> headers.

That *is* the problem.