Add a zstdmt which is equivalent as running zstd -T0

usr.bin/zstd/Makefile

@@ -16,9 +16,11 @@ CFLAGS+=	-I${SRCTOP}/contrib/zstd/programs \
 		-DHAVE_THREAD=1
 SCRIPTS=	zstdgrep
 LINKS=	${BINDIR}/zstd ${BINDIR}/unzstd \
-	${BINDIR}/zstd ${BINDIR}/zstdcat
+	${BINDIR}/zstd ${BINDIR}/zstdcat \
+	${BINDIR}/zstd ${BINDIR}/zstdmt
 MLINKS=	zstd.1 unzstd.1 \
-	zstd.1 zstdcat.1
+	zstd.1 zstdcat.1 \
+	zstd.1 zstdmt.1
 
 WARNS=	2
 LIBADD=	zstd