Bug 218850

The changes applied by configure-xcode-for-embedded-development leave Xcode in state where using @available in a Swift class breaks compilation of Objective-C methods marked with API_AVAILABLE that call into that class. Specifically, suppose we have: -a Swift class Foo marked @available(iOS 14.0, *) -an ObjC class Bar with a method myMethod marked API_AVAILABLE(ios(14)) The changes applied by configure-xcode-for-embedded-development for AvailabilityProhibitedInternal.h cause API_AVAILABLE to be ignored, but @available is not ignored. This means that calling from myMethod into Foo, which should be fine since both are available only in iOS 14+, results in a build failure when building with -Werror -Wunguarded-availability, since after pre-processing, myMethod has no availability notation. I ran into this when trying to build Chrome for iOS using the same Xcode that I use for building WebKit.