build: avoid to use ARMv5 machine flags by default

build: avoid to use ARMv5 machine flags by default

To use this flags it is encouraged to set TARGET_ARCH to "*v5*" from.
If unset, generic (buildsystem)'s flags will be used as expected.

I noticed this while building with Tizen:2.4:Mobile toolchain (gbs)
but it could also affect other ports or build infrastructures.

Bug: https://jira.iotivity.org/browse/IOT-694
Change-Id: I4bc279e809474bf664b4825f201df471c66a191c
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4541
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>