Rollup merge of rust-lang#70881 - eddyb:stage0-hide-incremental-unused-attrs, r=Mark-Simulacrum

bootstrap: work around "unused attribute" errors in incremental stdlib rebuilds. This should alleviate rust-lang#58633 separately from a proper fix. r? @Mark-Simulacrum

Author: Centril

src/bootstrap/builder.rs

@@ -1099,6 +1099,13 @@ impl<'a> Builder<'a> {
 
  if self.config.deny_warnings {
  rustflags.arg("-Dwarnings");
+
+ // FIXME(#58633) hide "unused attribute" errors in incremental
+ // builds of the standard library, as the underlying checks are
+ // not yet properly integrated with incremental recompilation.
+ if mode == Mode::Std && compiler.stage == 0 && self.config.incremental {
+ rustflags.arg("-Aunused-attributes");
+ }
  }
  }