swift234

IRGen: More robustly lay out enums with payloads.

John noted that LLVM's ABI rules for Integers of Unusual Size cause them to be aligned like the largest native integer type even inside packed structs, making them unsuited for byte-accurate layout in cases where the payload is a non-power-of-two size, so we have to bite the bullet and lay them out as arrays of i8, bitcasting to the payload type to load and store the payload and tag parts.

This still colors outside of the lines a bit because loading or storing e.g. an i72 is going to touch an i128's worth of memory. Baby steps. It'd be nice to be able to load and reconsistute the i72 without having to load and mask together all of the individual bytes.

Swift SVN r9058