Following the release of Xcode 7 / Beta 3, There's a Enable Bitcode in Build Settings which is set to YES, that prevents the Xcode project from compiling if it contains libraries that were not compiled with Xcode 7 / Beta 3 with the same build setting. Reference here
Bitcode is part of the app thinning initiative. Reference here
A temporary work around is to set this Enable Bitcode to NO, and the project will compile. However, eventually we should have all libraries recompiled with the latest Xcode, so that future projects are app thinning ready.
New tickets on rebuilding should be referenced to this ticket.