Fixed mkspecs/devices/linux_device_post.conf for non-arm platforms.

Now arm specific -mfloat-abi flag is added to compiler flags
only for arm architecture in linux_arm_device_post.conf.

Change-Id: Ie77ac6e0717d9d1fd9c14e1d6a26e86f08ab418c
Reviewed-by: Jarosław Staniek <staniek@kde.org>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>