Xcode: Fix test architecture selection for Xcode >= 5
In Tests/Architecture and Tests/BuildDepends/Project we select a set of OS X cpu architectures to use for the test. Prior to Xcode 4 we always used i386 and ppc. Starting with Xcode 4, the tools do not support ppc but do support x86_64, so we switch to that. Fix the version check to recognize Xcode >= 5 as at least Xcode 4 and use the new architectures.