test dangling ZST deref

Author: RalfJung

tests/compile-fail/dangling_zst_deref.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let p = {
+        let b = Box::new(42);
+        &*b as *const i32 as *const ()
+    };
+    let _x = unsafe { *p }; //~ ERROR dangling pointer was dereferenced
+}