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
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`.
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
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`.
auto merge of #17364 : thestinger/rust/debuginfo, r=pnkfelix

Closes #13611
auto merge of #17249 : vadimcn/rust/env-keys, r=alexcrichton

Closes #16937
configure: Remove support for i686-pc-mingw32 triple
mk: Remove check-fast target
jemalloc: Un-revert accidentally reverted jemalloc
auto merge of #17330 : brson/rust/bot-house-cleaning, r=alexcrichton

Both these things were transitionary until bot upgrades.