openpty module broken on Solaris

[Mats Erik Andersson]

The change introduced in gnulib-9fdffff is broken
on OpenSolaris and Solaris 11.

The reason is that said patch erroneously leads
to a claim

   /* config.h */
   # define HAVE_OPENPTY 1

This leads to an undefined linker reference
in "openpty.o" and thus also in "libgnu.a".

On behalf of GNU Inetutils,
   Mats Erik Andersson