Rollup of 7 pull requests

[Manishearth]

Successful merges:

• Move contributing.md to rustc-dev-guide and point at getting started #73454 (Move contributing.md to rustc-dev-guide and point at getting started)
• Use WASM's saturating casts if they are available #73724 (Use WASM's saturating casts if they are available)
• resolve: disallow labelled breaks/continues through closures/async blocks #73726 (resolve: disallow labelled breaks/continues through closures/async blocks)
• Update psm version #73781 (Update psm version)
• Update cargo, rls #73897 (Update cargo)
• Add option for local docker testing. #73952 (Add option for local docker testing.)
• disable BTree min_max test in Miri for now #73957 (disable BTree min_max test in Miri for now)

Failed merges:

r? @ghost

[Manishearth]

@rustbot modify labels: +rollup
@bors r+ rollup=never p=5

[bors]

📌 Commit e580b31 has been approved by Manishearth

[Manishearth]

This is a small rollup, but I don't expect this to pass, half the PRs in here are ones I consider very iffy. The goal is to sniff out any test failures, and let it land if there aren't, giving us a clean slate when it comes to iffy PRs.

[bors]

⌛ Testing commit e580b31 with merge e5a454d6bfedeb1d81472922479d5c47ad164ee3...

[bors]

💔 Test failed - checks-actions

[Manishearth]

2020-07-02T21:04:56.1997387Z �[0m�[1m�[38;5;9merror�[0m�[0m�[1m: this arithmetic operation will overflow�[0m
2020-07-02T21:04:56.1998277Z �[0m    �[0m�[0m�[1m�[38;5;12m--> �[0m�[0msrc/tools/cargo/src/cargo/core/compiler/fingerprint.rs:1967:21�[0m
2020-07-02T21:04:56.1998864Z �[0m     �[0m�[0m�[1m�[38;5;12m|�[0m
2020-07-02T21:04:56.2002872Z �[0m�[1m�[38;5;12m1967�[0m�[0m �[0m�[0m�[1m�[38;5;12m| �[0m�[0m            assert!(val >> 32 == 0);�[0m
2020-07-02T21:04:56.2004266Z �[0m     �[0m�[0m�[1m�[38;5;12m| �[0m�[0m                    �[0m�[0m�[1m�[38;5;9m^^^^^^^^^�[0m�[0m �[0m�[0m�[1m�[38;5;9mattempt to shift right by 32_i32 which would overflow�[0m
2020-07-02T21:04:56.2004924Z �[0m     �[0m�[0m�[1m�[38;5;12m|�[0m
2020-07-02T21:04:56.2005638Z �[0m     �[0m�[0m�[1m�[38;5;12m= �[0m�[0m�[1mnote�[0m�[0m: `#[deny(arithmetic_overflow)]` on by default�[0m
2020-07-02T21:04:56.2005849Z 
2020-07-02T21:04:57.0469347Z �[0m�[1m�[38;5;9merror�[0m�[0m�[1m: aborting due to previous error�[0m