Improve the zsh completions.

Currently the ZSH completions are quite old an nearly useless. This
brings them up to be compatible with current rust and makes them far
more useful.

Closes #17305
Relicense shootout-spectralnorm.rs to the shootout license

Everyone agreed.

Fix #17064
Relicense shootout-fasta.rs ti the shootout license.

Everyone agreed.

Fix #17072
Case-insensitive environment keys.
test: Un-ignore some GDB pretty printing tests

I've confirmed that these are working on the snapshot builders

Closes #16919
Add a forbid-output property in cfail tests
Pop the expansion context after expanding a method macro

We were leaving these on the stack, causing spurious backtraces.

I've confirmed that this test fails without the fix.
Remove unstable marker from std::rt

The `std::rt` module was marked `unstable` [a while
back](https://github.com/rust-lang/rust/commit/b6d4d117f4c2770649c7ddc2ad9ad4ce4c3b13b1),
and this change was not reverted when we moved to an `experimental`
baseline for `std`.
Fix warning and make code follow the text better
Document that CStrings live in the libc heap

Insists on the fact that the memory is managed by malloc
and not jemalloc
Closes #17067
librustc: Implement associated types behind a feature gate.

The implementation essentially desugars during type collection and AST
type conversion time into the parameter scheme we have now. Only fully
qualified names--e.g. `<T as Foo>::Bar`--are supported.
auto merge of #16377 : pcwalton/rust/associated-items, r=nikomatsakis

This is waiting on an RFC, but this basic functionality should be
straightforward. The implementation essentially desugars during type
collection and AST type conversion time into the parameter scheme we
have now.

r? @nikomatsakis
support LTO against libraries built with codegen-units > 1
auto merge of #17335 : TeXitoi/rust/relicense-shootout, r=brson

Everyone agreed.  Fix #17064, fix #17072 

@brson OK?
stop clamping the DWARF version to 3 on Linux

Closes #13611
auto merge of #17341 : alexcrichton/rust/unignore, r=brson

I've confirmed that these are working on the snapshot builders

Closes #16919
Pacify lint gods.
auto merge of #17349 : aturon/rust/rt-experimental, r=alexcrichton

The `std::rt` module was marked `unstable` [a while back](https://github.com/rust-lang/rust/commit/b6d4d117f4c2770649c7ddc2ad9ad4ce4c3b13b1), and this change was not reverted when we moved to an `experimental` baseline for `std`.
Document that CStrings live in the libc heap

Closes issue #17067 and improves pr #17355
auto merge of #17364 : thestinger/rust/debuginfo, r=pnkfelix

Closes #13611