pbuilder_pbx: disable bit code for Xcode projects

With Xcode7, Apple added support for compiling apps to bit code
instead of binary (*). But this is only supported when the deployment
target is at least 6.0. And in Qt-5.5, the deployment target is
still set to 5.1.1. The result is that every Qt application will fail
building once people move to Xcode7.

Instead of bumping the deployment target (which we plan to do
for Qt-5.6), we choose to switch off bit code for now.

 *: https://developer.apple.com/library/prerelease/ios/documentation/IDEs/Conceptual/AppDistributionGuide/AppThinning/AppThinning.html



Change-Id: I23001563439a7726506b7cd2dc77a82533b8a27b
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>