Slew of feature gating tests for issue rust-lang#43106.

src/test/compile-fail/feature-gate/issue-43106-gating-of-bench.rs

@@ -0,0 +1,25 @@
+// Copyright 2017 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.
+
+// error-pattern: main function not found
+
+// At time of authorship, a crate-level #![bench] with no `--test`
+// will cause compilation to error unconditionally with "main function
+// not found" (despite having one), similar to #[bench].
+//
+// (The non-crate level cases are in
+// issue-43106-gating-of-builtin-attrs.rs.)
+
+// See issue-12997-1.rs and issue-12997-2.rs to see how `#[bench]` is
+// handled in "weird places" when `--test` is passed.
+
+#![bench                   = "4100"]
+
+fn main() { }