third_party/heimdal_build: Determine whether time_t is signed

third_party/heimdal_build: Determine whether time_t is signed

Without this, Heimdal will assume time_t is unsigned, and a wrong
assumption will cause 'infinite' ticket lifetimes to be reckoned as from
the past, and thus requests will fail with KDC_ERR_NEVER_VALID.

This is an adaptation to Heimdal:

commit 9ae9902249732237aa1711591604a6adf24963fe
Author: Nicolas Williams <nico@twosigma.com>
Date:   Tue Feb 15 17:01:00 2022 -0600

    cf: Check if time_t is signed

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14995

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Tue Mar  1 18:07:50 UTC 2022 on sn-devel-184