rustc_error: make ErrorReported impossible to construct

There are a few places were we have to construct it, though, and a few
places that are more invasive to change. To do this, we create a
constructor with a long obvious name.

compiler/rustc_ast_lowering/src/lib.rs

@@ -952,7 +952,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 sess.diagnostic().delay_span_bug(
                                     span,
                                     "unexpected delimiter in key-value attribute's value",
-                                )
+                                );
                             }
                             unwrap_single_token(sess, tokens, span)
                         }