Auto merge of #87296 - Aaron1011:inert-warn, r=petrochenkov

Warn on inert attributes used on bang macro invocation

These attributes are currently discarded.
This may change in the future (see #63221), but for now,
placing inert attributes on a macro invocation does nothing,
so we should warn users about it.

Technically, it's possible for there to be attribute macro
on the same macro invocation (or at a higher scope), which
inspects the inert attribute. For example:

```rust
#[look_for_inline_attr]
#[inline]
my_macro!()

#[look_for_nested_inline]
mod foo { #[inline] my_macro!() }
```

However, this would be a very strange thing to do.
Anyone running into this can manually suppress the warning.

compiler/rustc_lint/src/context.rs

@@ -734,6 +734,16 @@ pub trait LintContext: Sized {
                         Applicability::MachineApplicable,
                     );
                 }
+                BuiltinLintDiagnostics::UnusedBuiltinAttribute {
+                    attr_name,
+                    macro_name,
+                    invoc_span
+                } => {
+                    db.span_note(
+                        invoc_span,
+                        &format!("the built-in attribute `{attr_name}` will be ignored, since it's applied to the macro invocation `{macro_name}`")
+                    );
+                }
             }
             // Rewrap `db`, and pass control to the user.
             decorate(LintDiagnosticBuilder::new(db));