Remove {As,Into,To}{Option,Either,Result} traits.

Expanded, that is:

- `AsOption`
- `IntoOption`
- `ToOption`
- `AsEither`
- `IntoEither`
- `ToEither`
- `AsResult`
- `IntoResult`
- `ToResult`

These were defined for each other but never *used* anywhere. They are
all trivial and so removal will have negligible effect upon anyone.
`Either` has fallen out of favour (and its implementation of these
traits of dubious semantics), `Option<T>` → `Result<T, ()>` was never
really useful and `Result<T, E>` → `Option<T>` should now be done with
`Result.ok()` (mirrored with `Result.err()` for even more usefulness).

In summary, there's really no point in any of these remaining.
Rename To{Str,Bytes}Consume traits to Into*.

That is:

- `ToStrConsume` → `IntoStr`;
- `ToBytesConsume` → `IntoBytes`.
Forbid multiple imports in use statements

Closes #10911
Move logic for test output generation forward

By performing this logic very late in the build process, it ended up leading to
bugs like those found in #10973 where certain stages of the build process
expected a particular output format which didn't end up being the case. In order
to fix this, the build output generation is moved very early in the build
process to the absolute first thing in phase 2.

Closes #10973
Remove workarounds from issue #4404

Closes #10875
std::vec: remove aliasing &mut [] and &[] from shift_opt.

Also, dramatically simplify it with some tasteful raw pointers, rather
than treating everything as a nail with `transmute`.
vec: avoid some unsafe code in MoveIterator's dtor
Update and un-xfail auto-encode test

Closes #6122
Spell out the units used for the `offset` argument, so that people do
not try to scale to units of bytes themselves.
auto merge of #11000 : cmr/rust/auto_encode, r=alexcrichton

Closes #6122
Remove obsolete mutability from ast::Ty
auto merge of #11002 : pnkfelix/rust/fsk-improve-doc-for-ptr-offset, r=alexcrichton

Spell out the units used for the `offset` argument, so that people do not try to scale to units of bytes themselves.
Detect stability attributes on methods.

If it's a trait method, this checks the stability attribute of the
method inside the trait definition. Otherwise, it checks the method
implementation itself.
std::vec::raw: convert init_elem to a method.
std::vec::raw: convert copy_memory to a method.
std::vec::bytes: remove the reference to overlapping src and dest in
docs for copy_memory.

&mut [u8] and &[u8] really shouldn't be overlapping at all (part of the
uniqueness/aliasing guarantee of &mut), so no point in encouraging it.
std::vec: convert .copy_memory to use copy_nonoverlapping_memory.

It is required that &mut[]s are disjoint from all other &(mut)[]s, so
this assumption is ok.
std::vec: make init_elem nicer by doing fewer moves.
Check even more live Path nodes in dead-code pass
provide an error at  at configure time if gcc, and g++ point to a mixture of clang and gcc. Fixes issue #10959

Signed-off-by: Carter Tazio Schonwald <carter.schonwald@gmail.com>