Use bool in favor of Option<()> for diagnostics

compiler/rustc_monomorphize/src/collector.rs

@@ -580,9 +580,9 @@ fn check_recursion_limit<'tcx>(
         let mut path = PathBuf::new();
         let was_written = if let Some(written_to_path) = written_to_path {
             path = written_to_path;
-            Some(())
+            true
         } else {
-            None
+            false
         };
         tcx.dcx().emit_fatal(RecursionLimit {
             span,

compiler/rustc_monomorphize/src/errors.rs

@@ -16,7 +16,7 @@ pub struct RecursionLimit {
     pub def_span: Span,
     pub def_path_str: String,
     #[note(monomorphize_written_to_path)]
-    pub was_written: Option<()>,
+    pub was_written: bool,
     pub path: PathBuf,
 }