swift234

IRGen: Expose APIs for asking about enum layout.

Export EnumImplStrategy from the GenEnum.h header, and add some accessors that LLDB or other interested parties can use to work out how an enum is laid out:

- getElementsWithPayload() and getElementsWithNoPayload(), to pick out the cases that were laid out as nonempty and empty (including those that are considered no-payload due to empty type optimization);

- getBitPatternForNoPayloadElement() to return the unique bit pattern representing a no-payload case; and

- getTagBitsForPayloads() to return the bitmask of the discriminator tag for payload cases.

Swift SVN r12269