crashes: add another test showing that everything works fine when we need compile-flags to repro an ice

Author: matthiaskrgr

tests/crashes/122909.rs

@@ -0,0 +1,13 @@
+//@ compile-flags: -Zpolymorphize=on -Zinline-mir=yes
+
+use std::sync::{Arc, Context, Weak};
+
+pub struct WeakOnce<T>();
+impl<T> WeakOnce<T> {
+    extern "rust-call" fn try_get(&self) -> Option<Arc<T>> {}
+
+    pub fn get(&self) -> Arc<T> {
+        self.try_get()
+            .unwrap_or_else(|| panic!("Singleton {} not available", std::any::type_name::<T>()))
+    }
+}