[Runtime] Look up Error bridging symbols indirectly through special symbols that won't be stripped in static builds.
[Runtime] Look up Error bridging symbols indirectly through special symbols that won't be stripped in static builds.

This fixes a problem where error bridging didn't work in stripped executables using the static versions of the Swift libraries. ErrorObject.mm looks up some symbols with dlsym, but stripping makes it so it can't find those. This change makes a separate set of symbols explicitly made for ErrorObject.mm to look up, and marks them as dynamically referenced so stripping won't remove them. Longer term, we'd like a better solution for looking up these symbols, but this will do for now.

rdar://problem/39810532
apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation