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_mir_transform/src/const_prop.rs

@@ -538,7 +538,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             self.tcx.struct_span_lint_hir(lint, lint_root, source_info.span, |lint| {
                 let mut err = lint.build(message);
                 err.span_label(source_info.span, format!("{:?}", panic));
-                err.emit()
+                err.emit();
             });
         }
     }