Swift and Objective-C both use LLVM to compile to native code. Both run on the Objective-C runtime.

• Understanding the Objective-C runtime - Cocoa Samurai
• What exactly is LLVM - StackOverflow
• Does Swift compile to native code? - Stack Overflow

• Build process of an iOS app - StackOverflow
• Apple Developer
  • Build Reference - A list of environment variables available during the build process.