Rollup merge of #71736 - RalfJung:silence-spurious-unused, r=Mark-Simulacrum

bootstrap: also apply unused-attributes hack without deny_warnings

This is a follow-up to https://github.com/rust-lang/rust/pull/70881 that also silences these warnings when deny_warnings is off. They otherwise spam my screen during development and make it hard to see actual warnings.

Cc  @eddyb r? @Mark-Simulacrum

src/bootstrap/builder.rs

@@ -1088,6 +1088,7 @@ 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
@@ -1096,7 +1097,6 @@ impl<'a> Builder<'a> {
                 rustflags.arg("-Aunused-attributes");
             }
         }
-        }
 
         if let Mode::Rustc | Mode::Codegen = mode {
             rustflags.arg("-Zunstable-options");