Remove incorrect debug assertions from catch_unwind

src/libstd/panicking.rs

@@ -286,11 +286,9 @@ pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>>
     );
 
     return if r == 0 {
-        debug_assert!(update_panic_count(0) == 0);
         Ok(ManuallyDrop::into_inner(data.r))
     } else {
         update_panic_count(-1);
-        debug_assert!(update_panic_count(0) == 0);
         Err(mem::transmute(raw::TraitObject {
             data: any_data as *mut _,
             vtable: any_vtable as *mut _,

src/test/ui/issues/issue-68696-catch-during-unwind.rs

@@ -0,0 +1,26 @@
+// Checks that catch_unwind can be used if unwinding is already in progress.
+// Used to fail when standard library had been compiled with debug assertions,
+// due to incorrect assumption that a current thread is not panicking when
+// entering the catch_unwind.
+//
+// run-pass
+// ignore-wasm       no panic support
+// ignore-emscripten no panic support
+
+use std::panic::catch_unwind;
+
+#[derive(Default)]
+struct Guard;
+
+impl Drop for Guard {
+    fn drop(&mut self) {
+        let _ = catch_unwind(|| {});
+    }
+}
+
+fn main() {
+    let _ = catch_unwind(|| {
+        let _guard = Guard::default();
+        panic!();
+    });
+}