swift234

Add new entry points to the enum implementation strategy for testing an enum against a
specific case and returning an i1 result.  This can be done a lot more efficiently (in
terms of generated LLVM IR) than doing a general switch over the cases.  This will be used
to implement rdar://19404937, but there is a miscompilation here that I'm tracking down.

Until it is working, I'm not committing the code to use these entrypoints, which wires it
into IRGen of SelectEnumInst and SelectEnumAddrInst.  Since that part isn't included, this
is NFC.


Swift SVN r24362