swift234

Eliminate race in swift_bridgeErrorToNSError.

Huge thanks to John for noting that 'consume' didn't provide the
guarantees we wanted, and to Michael G. for getting a TSan build up
and running to identify/verify this race.

It's possible that this is overlay strict, and that we only need to
look at the domain to ensure that the code and userInfo are
visible. However, TSan seems to prefix the form in this patch, so
we'll be more conservative for now.

Fixes rdar://problem/27541751.