Implement Default for the lint startup state by hand. std::sync::Once
implements Default only from Rust 1.100, so the derive fails on 1.99.

--- a/src/runtime/cli/lint_js.rs
+++ b/src/runtime/cli/lint_js.rs
@@ -407,7 +407,6 @@
 }
 
 /// Startup state that all VMs share.
-#[derive(Default)]
 struct Start {
     initialize: std::sync::Once,
     /// Set if the run won't have more than a few VMs. Stays unset if a VM starts before the files are known.
@@ -415,6 +414,17 @@
     memory: std::sync::OnceLock<usize>,
 }
 
+// `Once` implements `Default` only from Rust 1.100.
+impl Default for Start {
+    fn default() -> Self {
+        Self {
+            initialize: std::sync::Once::new(),
+            is_for_few: AtomicBool::default(),
+            memory: std::sync::OnceLock::new(),
+        }
+    }
+}
+
 impl Start {
     /// [`memory_for_engines`]
     fn memory(&self) -> usize {