switch arm ports to GCC 6.

this is the last GCC that will support these ports:
- epoc32
- netwinder
- shark
- acorn32
- cats
- most hpcarm systems (only NETBOOKPRO and WZERO3 remain)

share/mk/bsd.own.mk

@@ -1,4 +1,4 @@
-#	$NetBSD: bsd.own.mk,v 1.1043 2018/03/05 07:03:27 mrg Exp $
+#	$NetBSD: bsd.own.mk,v 1.1044 2018/03/05 08:08:06 mrg Exp $
 
 # This needs to be before bsd.init.mk
 .if defined(BSD_MK_COMPAT_FILE)
@@ -69,6 +69,7 @@ MKGCC?=		no
 HAVE_GCC?=	0
 .elif \
     ${MACHINE_CPU} == "alpha" || \
+    ${MACHINE_CPU} == "arm" || \
     ${MACHINE_CPU} == "hppa" || \
     ${MACHINE_CPU} == "ia64" || \
     ${MACHINE_CPU} == "i386" || \