feature request: allow packed types

[bnoordhuis]

Would it be possible to add support for packed types? Types appear to be unpacked right now (which is fine in itself) but it blocks interop with C APIs like epoll_wait.

Example: on x86_64, (0u32, 0u64) is 12 bytes when packed and 16 bytes when unpacked.

[brson]

While I do think we should support this in the language, you could probably hack around the problem with unsafe pointers.

[graydon]

I'm ok taking a patch to add packed as a prefix type operator to a record, vector or tuple type. It'll be a bit of a pain to support but does seem to be part of the world we live in.

[thestinger]

Fixed by cad2260