add test for issue #111353

Author: RalfJung

tests/ui/const_prop/ice-issue-111353.rs

@@ -0,0 +1,7 @@
+// build-pass
+#![crate_type = "lib"]
+#![feature(unsized_fn_params)]
+
+pub fn f(mut x: [i32]) {
+    x[0] = 1;
+}