This is a resurrection of rust-lang#40776, combining their Windows setup with an
additional setup on Unix to set the program group's niceness to +10
(low-but-not-lowest priority) when the `low_priority` option is on.

This PR does two things:
* Triggers an error on GNU/Linux & Android when /proc/self/exe doesn't exist
* Handle the error properly

… hashing.

As requested in rust-lang#29370.

…enabled

Signed-off-by: Marc-Antoine Perennou <[email protected]>

Introduce a new Installer object that hold a reference to all the
configured paths for installation

Signed-off-by: Marc-Antoine Perennou <[email protected]>

…r=steveklabnik

Add documentation for `ExitStatus`

As requested in rust-lang#29370. r? @steveklabnik

Improve the error management when /proc is not mounted

This PR does two things:
* Triggers an error on GNU/Linux & Android when /proc/self/exe doesn't exist
* Handle the error properly

rustbuild: install improvements

Install rust-analysis and rust-src to get in par with what we can get from rustup.
Allow bypassing the vendoring of dependencies. When we only build to install and not to redistribute dist tarballs, that part is not necessary, so avoid trying to install cargo-vendor.

…hton

Add an option to run rustbuild on low priority on Windows and Unix

This is a resurrection of rust-lang#40776, combining their Windows setup with an additional setup on Unix to set the program group's *nice*ness to +10 (low-but-not-lowest priority, mirroring the priority in the Windows setup) when the `low_priority` option is on.

misc doc improvements for std::env

fix typo in libstd/sync/mpsc/mod.rs docs

Fix regression introduced by jQuery removal

Fixes rust-lang#42078.
Follows rust-lang#41307.

r? @steveklabnik
cc @frewsxcv

…hes, r=eddyb

incr. comp.: Use more bits for DefPath hashes

Use 128 instead of 64 bits for DefPath hashes, like we do for everything else. Collision probability is unnecessarily high with 64 bits.

Also change the representation of `ich::Fingerprint` from `Fingerprint([u8; 16])` to `Fingerprint(u64, u64)` which is better for hashers like `FxHasher`.

…imulacrum

Update the Cargo submodules

More info [here](rust-lang#42070 (comment)) as to what's going on.

…lexcrichton

Fix x.py

Fixes rust-lang#42085