ldconfig: only configure compat32 when kernel supports it

and eliminate hard-coded arch list.

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D42669

libexec/rc/rc.d/ldconfig

@@ -39,10 +39,7 @@ ldconfig_start()
 		startmsg 'ELF ldconfig path:' ${_LDC}
 		${ldconfig} -elf ${_ins} ${_LDC}
 
-		machine_arch=$(sysctl -n hw.machine_arch)
-
-		case ${machine_arch} in
-		aarch64|amd64|powerpc64)
+		if check_kern_features compat_freebsd32; then
 			for i in ${ldconfig_local32_dirs}; do
 				if [ -d "${i}" ]; then
 					_files=`find ${i} -type f`
@@ -67,7 +64,7 @@ ldconfig_start()
 			startmsg '32-bit compatibility ldconfig path:' ${_LDC}
 			${ldconfig} -32 ${_ins} ${_LDC}
 			;;
-		esac
+		fi
 
 	fi
 }