Dependencies are still built after a build script error

E.g.

[package]

name = "a"
version = "0.0.1"
authors = []
build = "build.rs"

[dependencies.compile_msg]
git = "https://github.com/huonw/compile_msg"

fn main() { std::os::set_exit_status(1) }

$ cargo clean && cargo build
   Compiling a v0.0.1 (file:///home/huon/projects/test-rust/tmp/a)
   Compiling compile_msg v0.1.0 (https://github.com/huonw/compile_msg#569c6f18)
Build failed, waiting for other jobs to finish...
Failed to run custom build command for `a v0.0.1 (file:///home/huon/projects/test-rust/tmp/a)`
Process didn't exit successfully: `/home/huon/projects/test-rust/tmp/a/target/build/a-609ef28031a9b714/build-script-build` (status=1)

Dependencies could take a long time to compile (e.g. in servo), and fixing the problem raised by the build script may require adjustments that force many dependencies to be rebuild anyway, so it seems reasonable to at least give some indication that the build script failed immediately when it fails.

Reproduce the issue with the provided Cargo package, build.rs script, and cargo clean && cargo build command, then trace how Cargo handles a failed build script while dependency jobs are still running. Done means the failure is reported immediately and unnecessary dependency compilation does not continue after the script error.