"--json-output" is ignored by tool builds

[RalfJung]

When doing something like ./x.py build miri --json-output, then the errors/warnings in Miri itself are still reported in the normal, human-readable form, and not as JSON.

I assume something somewhere around here has to use a different function for running cargo, e.g. this one.

Cc @onur-ozkan

[onur-ozkan]

For tools, we handle the build results later even if they fail:

rust/src/bootstrap/src/core/build_steps/tool.rs

Lines 114 to 134 in 7717a30

	let build_success = builder.run_cmd(BootstrapCommand::from(&mut cargo).allow_failure());
	builder.save_toolstate(
	tool,
	if build_success { ToolState::TestFail } else { ToolState::BuildFail },
	);
	if !build_success {
	crate::exit!(1);
	} else {
	// HACK(#82501): on Windows, the tools directory gets added to PATH when running tests, and
	// compiletest confuses HTML tidy with the in-tree tidy. Name the in-tree tidy something
	// different so the problem doesn't come up.
	if tool == "tidy" {
	tool = "rust-tidy";
	}
	let cargo_out = builder.cargo_out(compiler, self.mode, target).join(exe(tool, target));
	let bin = builder.tools_dir(compiler).join(exe(tool, target));
	builder.copy_link(&cargo_out, &bin);
	bin
	}

compile::run_cargo doesn't provide that interface, but we can modify it to do so (since it uses compile::stream_cargo under the hood, which returns the command result without panicking).

[RalfJung]

All this toolstate stuff is not needed any more, though. We only use toolstate for books these days, so the tools can be cleaned up.

[RalfJung]

Thanks for the fix :)