Use Result::flatten in catch_with_exit_code

compiler/rustc_driver_impl/src/lib.rs

@@ -1249,8 +1249,7 @@ pub fn catch_fatal_errors<F: FnOnce() -> R, R>(f: F) -> Result<R, ErrorGuarantee
 /// Variant of `catch_fatal_errors` for the `interface::Result` return type
 /// that also computes the exit code.
 pub fn catch_with_exit_code(f: impl FnOnce() -> interface::Result<()>) -> i32 {
-    let result = catch_fatal_errors(f).and_then(|result| result);
-    match result {
+    match catch_fatal_errors(f).flatten() {
         Ok(()) => EXIT_SUCCESS,
         Err(_) => EXIT_FAILURE,
     }