WIP: iOS Building

This PR adds a build script for building RetroArch iOS.

This script supports building RetroArch for non-jailbroken and jailbroken phones.

It assumes you've already built the emulator cores via [libretro-super](https://github.com/libretro/libretro-super/blob/master/libretro-build-ios.sh)

More detailed information can be found in the [README](https://github.com/maddox/RetroArch/blob/ios-build-scripts/ios/README.md).

## iOS App

This includes a build script that will build just the iOS app. `script/build`.

By default, the app will be built with codesigning enabled. But you can disable this when running the script.

The resulting binary will be found in `ios/build/Release-iphoneos`

### With Codesigning

This will build the iOS app, codesign everything that needs to, and package it into a distributable IPA.

`script/build`

### Without Codesigning

This will simply build the app into a .app binary.

`NOCODESIGNING=true script/build`