* configure.ac: Simply check getpeerucred and ucred.h, and structure
members.
* agent/command-ssh.c: Include ucred.h.
(get_client_pid) [HAVE_STRUCT_SOCKPEERCRED_PID]: Use sockpeercred
structure for OpenBSD.
[LOCAL_PEERPID]: Use LOCAL_PEERPID for macOS.
[LOCAL_PEEREID]: Use LOCAL_PEEREID for NetBSD.
[HAVE_GETPEERUCRED]: Use getpeerucred for OpenSolaris.
--
This change also addresses following bug.
GnuPG-bug-id: 2981.
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>