Update Xcode project configuration

Switch from the classic `-parse-stdlib` option to the new `BuiltinModule` experimental feature.

Author: lorentey

Xcode/Atomics.xcconfig

@@ -28,7 +28,7 @@ VERSION_INFO_PREFIX =
 DYLIB_COMPATIBILITY_VERSION = $(CURRENT_PROJECT_VERSION)
 DYLIB_CURRENT_VERSION = $(CURRENT_PROJECT_VERSION)
 
-OTHER_SWIFT_FLAGS = $(inherited) -Xfrontend -parse-stdlib
+OTHER_SWIFT_FLAGS = $(inherited) -enable-experimental-feature BuiltinModule
 GCC_PREPROCESSOR_DEFINITIONS = $(inherited) ATOMICS_SINGLE_MODULE=1 ATOMICS_NATIVE_BUILTINS=1
 
 INSTALL_PATH = $(LOCAL_LIBRARY_DIR)/Frameworks