When building swift on macOS with long tests, the build would fail with
undefined references to these symbols. The undefined symbols were
expected to be present in swiftCore against which we link. However,
because the symbols are marked as internal, they would be dead stripped
before the dylib was constructed. As a result, we would end up with
undefined references to these symbols. Expose the additional internal
interfaces for now so that we can build the tests.
* [runtime] Clean up symbols in error machinery.
* [runtime] Clean up symbols in Foundation overlay.
* [runtime] Clean up symbols in collections and hashing.
* [runtime] Remove symbol controls from the Linux definition of swift_allocError.
* [tests] Add more stub functions for tests that link directly to the runtime.
If the Swift error wrapped in a _SwiftNativeNSError box conforms to
Hashable, the box now uses the Swift's conformance to Hashable.
Part of rdar://problem/27574348.
