autoconf cleanup for AC_FUNC_GETPGRP and GETPGRP_VOID

[Akim Demaille]

>>>>> "Paul" == Paul Eggert <eggert at twinsun.com> writes:

Paul> So here is a patch to simplify this ancient cruft so that it
Paul> works the way that Vile does things.  This patch shouldn't
Paul> require any change to any of the programs I looked into, but
Paul> I'll CC: this to bug-bash, bug-gawk, and openssh-unix-dev to
Paul> give them a heads-up.

Install whenever you want.  Thanks!