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_lint/src/early.rs

@@ -45,7 +45,9 @@ impl<'a, T: EarlyLintPass> EarlyContextAndPass<'a, T> {
             self.context.lookup_with_diagnostics(
                 lint_id.lint,
                 Some(span),
-                |lint| lint.build(&msg).emit(),
+                |lint| {
+                    lint.build(&msg).emit();
+                },
                 diagnostic,
             );
         }