Starting with Xcode 4.5 the possibility of building for armv6 devices is not given anymore (iPhone/iPod touch 1st and 2nd generation). This means no new versions of our app for iPhone 2G and 3G which is very unlucky. Does anyone know if there will be a workaround? I really don´t see any technical reasons for this.
You can have multiple versions of xcode installed. In the past, that has been the fix needing to use an older xcode feature.
It is a workaround, and the project files may eventually evolve in a way that no longer supports the older tools, but for the time being, that will allow you to build for older targets.
If you have a single project that you want to work with in both versions of XCode, then you may end up having to manage separate project control files via source control tricks and/or file shuffling.
I would also recommend that project structure changes and binary file management (e.g. Core Data models) happen via the old version, as XCode 4.5 will be backward compatible, but forward compat is rarely assured.
There's another solution I found in chpwn blog: Building for armv6 in Xcode 4.5.
This allows you to work with Xcode 4.5 but compile using 5.1 SDK.
The downside: you can’t use the iOS 6 SDK when using this trick, and you can’t build for armv7s.
Yes, there are workarounds. If you need to actually take advantage of new iOS 6 features, try either of the first couple answers to this related question. The first answer requires using both Xcode 4.4 and 4.5. If you never want to have to open Xcode 4.4, then use the second answer.
If you just want to be able to build an executable in Xcode 4.5 that works on armv6, armv7 and armv7s devices, without actually taking advantage of new iOS 6 SDK APIs, then you can see my answer to another question, which is much simpler ... but has the limitation that you can't take advantage of new iOS 6 features on iOS 6 devices.
You can add the string "armv6 armv7" as architecture. Do not select a predefined setting.
来源：https://stackoverflow.com/questions/12474870/ios-is-there-absolutely-no-way-to-build-for-armv6-in-xcode-4-5