bootstrap: clear miri's ui test deps when rustc changes

[RalfJung]

@onur-ozkan I hope this makes sense... it's quite hard to test this, but it did at least cause one rebuild of the right files for me, and then it doesn't seem to keep rebuilding, so at first sight this look at least better than the status quo.

[rustbot]

r? @Kobzol

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[Kobzol]

r? @onur-ozkan

[RalfJung]

rust-lang/miri#3790 makes us use a Miri-specific folder.

[RalfJung]

@rustbot ready

[onur-ozkan]

@bors r+ rollup

[bors]

📌 Commit 2b584dc has been approved by onur-ozkan

It is now in the queue for this repository.

[RalfJung]

I'm afraid only clearing when rustc changes isn't enough... we need to also clear whenever the Miri sysroot gets rebuilt. Cargo doesn't seem to recognize that the standard library changes, and then we still get build failures as before.

I don't know a good way to implement that, though...

[onur-ozkan]

We could clear it unconditionally in a similar way to how we handle docs:

rust/src/bootstrap/src/core/builder.rs

Lines 1495 to 1510 in 730d5d4

	if cmd_kind == Kind::Doc{
	let my_out = match mode {
	// This is the intended out directory for compiler documentation.
	Mode::Rustc | Mode::ToolRustc => self.compiler_doc_out(target),
	Mode::Std => {
	ifself.config.cmd.json(){
	out_dir.join(target.triple).join("json-doc")
	}else{
	out_dir.join(target.triple).join("doc")
	}
	}
	_ => panic!("doc mode {mode:?} not expected"),
	};
	let rustdoc = self.rustdoc(compiler);
	self.clear_if_dirty(&my_out,&rustdoc);
	}