Pre-RFC: Orthogonal Discriminants

Summary Right now the layout algorithm is mixed up with the type of the discriminant. This RFC splits those up better for more flexibilty and new functionality. Motivation Quick! What's the difference between #[repr(Rust, u32)], #[repr(u32)], and #[repr(C, u32)]? What does #[repr(u128)] do in Rust 1.14? What does #[repr(u48)] do in Rust 1.138? Why is mem::Discriminant<Option<u8>> bigger than Option<u8>? How can I make a c_long discrinant? Is enum Foo { A = 2222222222 } something you're allow...