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`.
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.