[workspaces/xcode] Make all targets build + iOS target (OSX 10.8.3 + Xcode 4.6.1)

Hi,

I fixed the 4 build configurations in workspaces/xcode and added a 5th one for iOS.

Notable changes:
- All builds now use Apple LLVM compiler (Clang)
- Builds using boost require boost to be in /usr/local (e.g. `brew install boost`)