swift234

IRGen: Use packed structs to accurately lay out aggregate types.

LLVM's normal data layout doesn't jive with our own StructLayout's more aggressive use of padding space, and causes problems such as <rdar://problem/14336903>. Because we do our own alignment and stride management, we can safely use LLVM packed struct types with manual padding to get the level of control we need to accurately reflect our desired struct layout.

Swift SVN r9056