Add ./x.py check src/{libstd,libtest,librustc}

[Mark-Simulacrum]

This currently only supports a limited subset of the full compilation,
but is likely 90% of what people will want and is possible without
building a full compiler (and also building LLVM). In theory, this means
that contributors who don't want to build LLVM now have an easy way to
compile locally, though running tests won't work.

[Mark-Simulacrum]

cc @rust-lang/compiler

r? @alexcrichton

[kennytm]

Checking in non-stage-0 may still be useful if we want to check libstd after some new semantic is implemented:

./x.py build --stage 0 src/librustc
./x.py check --keep-stage 1 --stage 1 src/libstd
# edit
./x.py check --keep-stage 1 --stage 1 src/libstd
# edit
./x.py check --keep-stage 1 --stage 1 src/libstd

[michaelwoerister]

What exactly do these do?

[Mark-Simulacrum]

This runs cargo check instead of cargo build which nets much faster builds. Currently only works with stage 0, though we could technically expand it to work with any stage.

[michaelwoerister]

OK, that's great!

[bors]

☔ The latest upstream changes (presumably #47528) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

Oops sorry about that, looks great to me!

r=me

[Mark-Simulacrum]

@bors r=alexcrichton

[bors]

📌 Commit 7319232 has been approved by alexcrichton

[matklad]

Should this option be mentioned in https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#the-build-system?

[Mark-Simulacrum]

Probably, yes. I'll open an issue.

[bors]

☔ The latest upstream changes (presumably #47678) made this pull request unmergeable. Please resolve the merge conflicts.

[Mark-Simulacrum]

@bors r=alexcrichton

[bors]

📌 Commit 6aeb1cf has been approved by alexcrichton