message: llvm::CodeModel::Default went away, we were using it...
  Replace the use of Default in SwiftASTContext.cpp with llvm::None,
  which mirrors the change to the clang side of lldb done when Default
  was deleted.
  <rdar://problem/33735883>
diff: @@ -4583,7 +4583,7 @@ swift::irgen::IRGenModule &SwiftASTContext::GetIRGenModule() {
  "", // features
  *getTargetOptions(),
  llvm::Reloc::Static, // TODO verify with Sean, Default went away
  - llvm::CodeModel::Default, optimization_level);
  + llvm::None, optimization_level);
  if (target_machine) {
  // Set the module's string representation.
  const llvm::DataLayout data_layout = target_machine->createDataLayout();
  