relates to:

• SR-7051 Compiler fails with "Module not found" error

Issue Description:

A Swift module that defines private or internal extensions on a public Objective-C type will export that extension publicly through its `-Swift` compatibility header.

FooObjectExtensions.swift:

import FooModule

extension FooObject {
    func doThing()
}

BarModule-Swift.h:

@import Foo;

@interface FooObject (SWIFT_EXTENSION(BarModule))
@end

This is problematic because private dependencies are exposed as `@import`s to the outside through the compatiblity header. The compatibility header generator should remove extensions that have empty bodies.