Missing openpty / stropt.h

[Robbert Haarman]

Building Gambit (http://www.iro.umontreal.ca/~gambit/) on OpenBSD fails 
due to a missing stropt.h header file. However, this file is only looked 
for when HAVE_openpty is unset. OpenBSD 3.8 includes a manpage for 
openpty, however, the function does not appear to be included in the C 
library. Is there some other library that has to be included to get this 
functionality? None seems to be mentioned in the manpage.