This can eventually be made more efficient by avoiding copies in all the
callees, but this is the minimal fix. Remove an unnecessary bit of
reverse-dependency on the Foundation overlay while we're here.
rdar://34222540
Deprecated the `PlaygroundQuickLook` enum and `CustomPlaygroundQuickLookable`
protocol. These are being targeted for removal in Swift 5, so we want to
unconditionally deprecate them now to encourage use of
`CustomPlaygroundDisplayConvertible` instead.
This commit includes deprecated the various `CustomPlaygroundQuickLookable`
conformances across the standard library and overlay libraries.
* [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.
