Clang compiling, gnu11 support and simulator fixes (i386, x86_64)

### Changes
- Added support for compiling with clang as the default (faster, more optimised, smaller, supports c11+c14) (does a bit more than the gcc restricted clang compile)
- Added variable at the top to make this (Configurable)
- Also stepped the default C standard to gnu11 (asm and other flags still work however get all the benefits of c11 standard) (Configurable) 
- Fixes configure issues for i386 #36  
- Fixes simulator minimum iOS target problems from incorrect min tag being used (which was bypassed by selecting the latest iOS target) See #35 
- Added .gitignore for common Xcode file when running the project
- Set Optimisation level at -Os (clang supports)

### Testing
- Tested on i386, x86_64 (simulators) and  armv7, arm64 (devices)