diff3: Move to own package

diff3 is the last remaining GPL-licensed userland component.  Move it
to its own package, so that it may be excluded if desired.

Reviewed by:	ivy
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52810

(cherry picked from commit e7258c4252)

gnu/usr.bin/diff3/Makefile

@@ -1,8 +1,9 @@
+PACKAGE= diff3
+
 DIFFSRC=${SRCTOP}/contrib/diff/src
 .PATH:  ${DIFFSRC} \
 	${SRCTOP}/contrib/diff/lib \
 	${SRCTOP}/contrib/diff/man
-
 PROG=		diff3
 SRCS=           diff3.c version-etc.c \
 		xmalloc.c error.c c-stack.c exitfail.c cmpbuf.c

release/packages/ucl/diff3-all.ucl

@@ -0,0 +1,15 @@
+/*
+ * SPDX-License-Identifier: ISC
+ */
+
+comment = "GNU 3-way file comparison and merge utility"
+
+desc = <<EOD
+Compares three files line by line, optionally merging them.
+EOD
+
+licenses = [ "GPL-2.0-or-later" ]
+
+annotations {
+	set = "optional,optional-jail"
+}