Adding compile fail test for const_indexing feature

src/test/compile-fail/feature-gate-const-indexing.rs

@@ -0,0 +1,17 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+fn main() {
+    const ARR: [i32; 6] = [42, 43, 44, 45, 46, 47];
+    const IDX: usize = 3;
+    const VAL: i32 = ARR[IDX];
+    const BLUB: [i32; (ARR[0] - 41) as usize] = [5]; //~ ERROR constant evaluation error
+}

src/tools/tidy/src/features.rs

@@ -167,7 +167,7 @@ pub fn check(path: &Path, bad: &mut bool) {
     // FIXME get this whitelist empty.
     let whitelist = vec![
         "abi_ptx", "simd", "static_recursion",
-        "cfg_target_has_atomic", "staged_api", "const_indexing",
+        "cfg_target_has_atomic", "staged_api",
         "unboxed_closures", "stmt_expr_attributes",
         "cfg_target_thread_local", "unwind_attributes",
         "inclusive_range_syntax"