Detect bare blocks with type ascription that were meant to be a struct literal

Address part of #34255.

Potential improvement: silence the other knock down errors in
`issue-34255-1.rs`.

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -102,6 +102,7 @@ fn call_unreachable(cx: &ExtCtxt<'_>, span: Span) -> P<ast::Expr> {
         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
         span,
         tokens: None,
+        could_be_bare_literal: false,
     }))
 }