mk: remove -fno-omit-frame-pointer

This is still used for Rust code (`Options.NoFramePointerElim = true`).
Rename CopyableVector to CloneableVector
Rename OwnedCopyableVector to OwnedCloneableVector
Rename ImmutableCopyableVector to ImmutableCloneableVector
Rename CopyableTuple to CloneableTuple
Implement an unused_result lint

I attempted to implement the lint in two steps. My first attempt was a
default-warn lint about *all* unused results. While this attempt did indeed find
many possible bugs, I felt that the false-positive rate was too high to be
turned on by default for all of Rust.

My second attempt was to make unused-result a default-allow lint, but allow
certain types to opt-in to the notion of "you must use this". For example, the
Result type is now flagged with #[must_use]. This lint about "must use" types is
warn by default (it's different from unused-result).

The unused_must_use lint had a 100% hit rate in the compiler, but there's not
that many places that return Result right now. I believe that this lint is a
crucial step towards moving away from conditions for I/O (because all I/O will
return Result by default). I'm worried that this lint is a little too specific
to Result itself, but I believe that the false positive rate for the
unused_result lint is too high to make it useful when turned on by default.
Document vector destructuring with wildcard '..'
Treat unary struct and enum variants as rvalues

Closes #11681
Removing do keyword from librustdoc
Removing do keyword from libstd and librustc
Remove do keyword from librustuv
Removing do keyword from libnative
Removing do keyword from librustpkg
Removing do keyword from libextra
Removing do keyword from libgreen
Remove do keyword from test/
Remove do keyword from compiletests
Removing usage of the do keyword from documentation
Removing support for the do syntax from libsyntax and librustc.

Fixes #10815.
auto merge of #11868 : bytbox/rust/remove-do, r=alexcrichton

Fixes #10815.