buildroot

package/efl: bump to 1.17.2

Update the untested configuration warning option.

Disable efl build for host/target gcc older than 4.7 (oldest tested version).
http://lists.busybox.net/pipermail/buildroot/2016-June/163606.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>