auto merge of #8285 : huonw/rust/deriving+++, r=alexcrichton

Some general clean-up relating to deriving:
- `TotalOrd` was too eager, and evaluated the `.cmp` call for every field, even if it could short-circuit earlier.
- the pointer types didn't have impls for `TotalOrd` or `TotalEq`.
- the Makefiles didn't reach deep enough into libsyntax for dependencies.

(Split out from https://github.com/mozilla/rust/pull/8258.)