Add option to build scripts to override build type, so it can be
freely chosen.
Build in release mode on GitHub - RelWithDebInfo was too big.
Amends b1640074e3
Change-Id: Ibba6e60d4e9b2eee24e789bfd28bddffb1e782f6
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>