Right now we represent the () type as a one bit integer. () shouldn't take up any space.

In theory we should be able to use an empty llvm struct type, but there are some issues that come up.

Making that change doesn't actually just work. Compiling with optimization, LLVM decides that assigning () to a local is undefined behavior because we do a zero length memset to an invalid address.

Compiling without optimization, we crash in some of the hashtable drop glue.