GCC is no longer used for iOS development so forcing it doesn't work properly anymore.
Fixes to deal with architecture availability in Xcode 6.x.   32 bit support probably won't be supported at all in the relatively near future as no 32 bit OSes are supported at this stage. (10.6 is last 32 bit kernel)
Added ARCHS_OVERRIDE option which allows custom architecture targets to be selected instead of the native defaults, currently only applies to OS X and iOS builds
Tweak to only override CMAKE_OSX_ARCHITECTURES if its not set
Better handling of default values for CMAKE_OSX_ARCHITECTURES and allowing for override.  Rather than the Xcode default of only building for the current platform, universal binaries are always built.

Use CMAKE_OSX_ARCHITECTURES environment variable to CMake to specify the archs to build, or -DBUILD_UNIVERSAL_BINARIES=OFF argument to cmake to use Xcode default values
Merge pull request #230 from libRocket/feature/xcode6-fixes

Fixes for OS X and iOS builds with Xcode 6