Add regression test for const generics ICE

Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>

src/test/ui/const-generics/const-generic-array-wrapper.rs

@@ -0,0 +1,18 @@
+// run-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct Foo<T, const N: usize>([T; {N}]);
+
+impl<T, const N: usize> Foo<T, {N}> {
+    fn foo(&self) -> usize {
+        {N}
+    }
+}
+
+fn main() {
+    let foo = Foo([0u32; 21]);
+    assert_eq!(foo.0, [0u32; 21]);
+    assert_eq!(foo.foo(), 21);
+}

src/test/ui/const-generics/const-generic-array-wrapper.stderr

@@ -0,0 +1,6 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/const-generic-array-wrapper.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+