"Has not been ported to" usually isn't quite correct these days.
Eg it could be an old platform that we dropped support for.
+2014-03-05 Glenn Morris <rgm@gnu.org>
+
+ * configure.ac: Tweak the "unported" error message.
+
2014-03-05 Paul Eggert <eggert@cs.ucla.edu>
Fix configuration bug on Solaris 2.5.1 (Bug#16905).
dnl quotation ends
if test $unported = yes; then
- AC_MSG_ERROR([Emacs hasn't been ported to `${canonical}' systems.
+ AC_MSG_ERROR([Emacs does not support building on `${canonical}' systems.
+If you think it should, please send a report to bug-gnu-emacs@gnu.org.
Check `etc/MACHINES' for recognized configuration names.])
fi