SPDX: Tag BSD-4.3TAHOE

TIL traceroute.8 has one of the oldest liceses, predating BSD-4-Clause!
The SPDX tag was not even on Wikipedia. These are all the files I could
find in the tree with git grep that look like the license reported on
the SPDX website, including one that was misfiled.

Ref:			https://spdx.org/licenses/BSD-4.3TAHOE.html
MFC after:		3 days
Reported by:		brooks
Reviewed by:		brooks, carlavilla, imp, ivy
Approved by:		carlavilla (mentor)
Differential Revision:	https://reviews.freebsd.org/D50362

lib/libc/stdtime/strftime.c

@@ -1,4 +1,6 @@
 /*
+ * SPDX-License-Identifier: BSD-4.3TAHOE
+ *
  * Copyright (c) 1989 The Regents of the University of California.
  * All rights reserved.
  *

usr.sbin/cron/cron/popen.c

@@ -1,4 +1,6 @@
 /*
+ * SPDX-License-Identifier: BSD-4.3TAHOE
+ *
  * Copyright (c) 1988 The Regents of the University of California.
  * All rights reserved.
  *

usr.sbin/ppp/arp.c

@@ -2,7 +2,7 @@
  * sys-bsd.c - System-dependent procedures for setting up
  * PPP interfaces on bsd-4.4-ish systems (including 386BSD, NetBSD, etc.)
  *
- * SPDX-License-Identifier: BSD-1-Clause
+ * SPDX-License-Identifier: BSD-4.3TAHOE
  *
  * Copyright (c) 1989 Carnegie Mellon University.
  * All rights reserved.

usr.sbin/traceroute/traceroute.8

@@ -1,3 +1,6 @@
+.\"
+.\" SPDX-License-Identifier: BSD-4.3TAHOE
+.\"
 .\" Copyright (c) 1989, 1995, 1996, 1997, 1999, 2000
 .\"	The Regents of the University of California.  All rights reserved.
 .\"