How to build against older iOS versions with the latest Xcode downloads?

Question

I have multiple versions of Xcode installed. I can build my project against older iOS versions by launching old Xcode. But how could I use newer Xcode versions to build agai

Answer 1

This became harder in Xcode 3.2.5 (iOS 4.2.1) as the separate "Base SDK" values for Device and Simulator are replaced with a single "iOS SDK".

See my post in Xcode/Simulator: How to run older iOS version? for details on how to access older Simulator SDK versions in this latest Xcode.