compiletest should validate `only-` headers

[wesleywiser]

The failure mode for using an unrecognized header like only-i686 is that the test never runs which is very easy to miss. compiletest should verify that it recognizes the header value and that some target could run the test. This is basically a more specific version of #83551.

See #90569 for a case where this would have caught tests that never ran.

This is where the changes will need to be made:

rust/src/tools/compiletest/src/header.rs

Lines 674 to 713 in 27143a9

	fn parse_cfg_name_directive(&self, line: &str, prefix: &str) -> ParsedNameDirective {
	if !line.as_bytes().starts_with(prefix.as_bytes()) {
	return ParsedNameDirective::NoMatch;
	}
	if line.as_bytes().get(prefix.len()) != Some(&b'-') {
	return ParsedNameDirective::NoMatch;
	}
	let name = line[prefix.len() + 1..].split(&[':', ' '][..]).next().unwrap();
	let is_match = name == "test" ||
	self.target == name || // triple
	util::matches_os(&self.target, name) || // target
	util::matches_env(&self.target, name) || // env
	self.target.ends_with(name) || // target and env
	name == util::get_arch(&self.target) || // architecture
	name == util::get_pointer_width(&self.target) || // pointer width
	name == self.stage_id.split('-').next().unwrap() || // stage
	name == self.channel || // channel
	(self.target != self.host && name == "cross-compile") ||
	(name == "endian-big" && util::is_big_endian(&self.target)) ||
	(self.remote_test_client.is_some() && name == "remote") ||
	match self.compare_mode {
	Some(CompareMode::Nll) => name == "compare-mode-nll",
	Some(CompareMode::Polonius) => name == "compare-mode-polonius",
	Some(CompareMode::Chalk) => name == "compare-mode-chalk",
	Some(CompareMode::SplitDwarf) => name == "compare-mode-split-dwarf",
	Some(CompareMode::SplitDwarfSingle) => name == "compare-mode-split-dwarf-single",
	None => false,
	} ||
	(cfg!(debug_assertions) && name == "debug") ||
	match self.debugger {
	Some(Debugger::Cdb) => name == "cdb",
	Some(Debugger::Gdb) => name == "gdb",
	Some(Debugger::Lldb) => name == "lldb",
	None => false,
	};
	if is_match { ParsedNameDirective::Match } else { ParsedNameDirective::NoMatch }
	}

[jieyouxu]

compiletest does validate only-* headers now, e.g.

rust/src/tools/compiletest/src/header/cfg.rs

Lines 102 to 106 in eeeb021

	condition! {
	name: &config.target,
	allowed_names: &target_cfgs.all_targets,
	message: "when the target is {name}"
	}

Closing this issue as it has been addressed in compiletest.