59ba8024af
Remove `ffi_returns_twice` feature The [tracking issue](https://github.com/rust-lang/rust/issues/58314) and [RFC](https://github.com/rust-lang/rfcs/pull/2633) have been closed for a couple of years. There is also an attribute gate in R-A which should be removed if this lands.
The codegen crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.