Fix QNX 6.6 build

The stdlib of the upcoming QNX 6.6 has this abs overload,
so check for the version when redefining it.

Change-Id: Ib5650226c65417b42d8d7a79fac7ca53d3f315f1
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Reviewed-by: Andreas Holzammer <andreas.holzammer@kdab.com>
Reviewed-by: Bernd Weimer <bweimer@blackberry.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>