Technically, these operations belong in the ObjectiveC module, where NSObject
is defined. Keep them there. However, we need to build the mock ObjectiveC
overlay with `-disable-objc-attr-requires-foundation-module` now.
Don't allow types conforming to 'Error' or protocol compositions
involving 'Error' to be reflected in Objective-C. We still allow
bridging conversions, but they are not statically bridged. Fixes
SR-2249/rdar://problem/27658940.