add test that repeating non-Copy constants works

src/test/ui/consts/rfc-2203-const-array-repeat-exprs/const-repeat.rs

@@ -0,0 +1,13 @@
+// check-pass
+
+// Repeating a *constant* of non-Copy type (not just a constant expression) is already stable.
+
+const EMPTY: Vec<i32> = Vec::new();
+
+pub fn bar() -> [Vec<i32>; 2] {
+    [EMPTY; 2]
+}
+
+fn main() {
+    let x = bar();
+}