Fix x fix on the standard library itself

Author: jyn514

src/bootstrap/check.rs

@@ -99,6 +99,10 @@ impl Step for Std {
             cargo_subcommand(builder.kind),
         );
         std_cargo(builder, target, compiler.stage, &mut cargo);
+        if matches!(builder.config.cmd, Subcommand::Fix { .. }) {
+            // By default, cargo tries to fix all targets. Tell it not to fix tests until we've added `test` to the sysroot.
+            cargo.arg("--lib");
+        }
 
         builder.info(&format!(
             "Checking stage{} library artifacts ({} -> {})",