Avoid manually producing FatalError in a couple of places

compiler/rustc_driver_impl/src/lib.rs

@@ -1024,7 +1024,7 @@ pub fn describe_flag_categories(early_dcx: &EarlyDiagCtxt, matches: &Matches) ->
     let wall = matches.opt_strs("W");
     if wall.iter().any(|x| *x == "all") {
         print_wall_help();
-        rustc_errors::FatalError.raise();
+        return true;
     }
 
     // Don't handle -W help here, because we might first load additional lints.

compiler/rustc_errors/src/lib.rs

@@ -1048,8 +1048,8 @@ impl<'a> DiagCtxtHandle<'a> {
     /// bad results, such as spurious/uninteresting additional errors -- when
     /// returning an error `Result` is difficult.
     pub fn abort_if_errors(&self) {
-        if self.has_errors().is_some() {
-            FatalError.raise();
+        if let Some(guar) = self.has_errors() {
+            guar.raise_fatal();
         }
     }