Resurrect standalone command

While command(1) is now classified by POSIX as an intrinsic utility and
no longer required to exist as a standalone program, it turns out that
we still have a use for it (cf. env(1)), so resurrect it.

PR:		291879
Fixes:		4100bd6caa ("usr.bin: Remove intrinsic utilities")
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D54341

ObsoleteFiles.inc

@@ -55,7 +55,6 @@
 OLD_FILES+=usr/bin/alias
 OLD_FILES+=usr/bin/bg
 OLD_FILES+=usr/bin/cd
-OLD_FILES+=usr/bin/command
 OLD_FILES+=usr/bin/fc
 OLD_FILES+=usr/bin/fg
 OLD_FILES+=usr/bin/getopts

usr.bin/Makefile

@@ -23,6 +23,7 @@ SUBDIR=	apply \
 	colrm \
 	column \
 	comm \
+	command \
 	compress \
 	csplit \
 	ctlstat \

usr.bin/command/Makefile

@@ -0,0 +1,4 @@
+SCRIPTS=command.sh
+MAN=
+
+.include <bsd.prog.mk>

usr.bin/command/command.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+builtin command "$@"