swift234

IRGen: Fix layout bug with payloaded enums.

If the enum gets laid out with a non-power-of-two payload and an extra tag, such as { i72, i2 }, then LLVM's natural location for the extra tag is going to be different from where we actually want it, so let's do our own byte offset calculation by bitcasting to i8* and gepping instead of trying to gep the struct directly.

Swift SVN r9023