Generate yarp libraries about iyarp

[francesco-romano]

With further modifications of the toolchain file it is now possible to generate an Xcode project.
Unfortunately the generated project hardcode the SDK path and the architectures yielding the impossibility to build the yarp for both the simulator and the device. This can be manually solved by opening the project.
We should find an automated way to achieve this if possible.

[francesco-romano]

About the last task a PR has been opened on yarp: robotology/yarp#535

[francesco-romano]

Updated toolchain, and added to the repository.
The cmake file has been taken from https://github.com/cristeab/ios-cmake, with in turn comes from the original google code hosted project.
The toolchain file has been modified to enable compilation with GNU Makefiles (slight modifications), and to work with Xcode project (compiler detection and SDK detection taken from LLVM toolchain files) plus some modification to make it working.
Future versions of cmake should be even more compatible with Xcode projects.