Make type_is_immediate not depend on LLVM.
Make type_is_immediate not depend on LLVM.

This has the nice benefit of making it much simpler to work with,
since it now consists of a single match statement.

GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust