Adds iOS 6.0, which is now the default.
- changed the default iOS SDK to version 6.0
- use xcrun to locate the selected compiler
- added armv7s as an option for architecture
- made armv7 + armv7s the default architecture
- renamed the LLVM compiler option to LLVM_GNU for clarity
since LLVM is naturally associated with CLANG
Tom Pelaia II and Mark Engbretson contributed the build configuration
and OS-dependent files, I modified the build config to bring it up to
R3.14.12 standards and added the Release Notes.