Run expand-yaml-anchors in x test tidy

Previously, the pre-commit hook which runs `x test tidy` could pass only to have CI fail within the first 30 seconds.
This adds about 30 seconds to `test tidy` (for an initial run, much less after the tool is built the first time)
in exchange for catching errors in `.github/workflows/ci.yml` before they're pushed.

Author: jyn514

src/bootstrap/test.rs

@@ -1114,9 +1114,6 @@ impl Step for Tidy {
             cmd.arg("--bless");
         }
 
-        builder.info("tidy check");
-        try_run(builder, &mut cmd);
-
         if builder.config.channel == "dev" || builder.config.channel == "nightly" {
             builder.info("fmt check");
             if builder.initial_rustfmt().is_none() {
@@ -1134,6 +1131,11 @@ help: to skip test's attempt to check tidiness, pass `--exclude src/tools/tidy`
             }
             crate::format::format(&builder, !builder.config.cmd.bless(), &[]);
         }
+
+        builder.info("tidy check");
+        try_run(builder, &mut cmd);
+
+        builder.ensure(ExpandYamlAnchors {});
     }
 
     fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {

src/tools/expand-yaml-anchors/src/main.rs

@@ -51,7 +51,7 @@ impl App {
             ["generate", ref base] => (Mode::Generate, PathBuf::from(base)),
             ["check", ref base] => (Mode::Check, PathBuf::from(base)),
             _ => {
-                eprintln!("usage: expand-yaml-anchors <source-dir> <dest-dir>");
+                eprintln!("usage: expand-yaml-anchors <generate|check> <base-dir>");
                 std::process::exit(1);
             }
         };