rollup merge of #22116: kmcallister/cfg_attr

Fixes #22070.
Fixes #19372.

r? @sfackler

src/test/compile-fail/cfg-attr-cfg-2.rs

@@ -0,0 +1,18 @@
+// 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.
+//
+// error-pattern: main function not found
+// compile-flags: --cfg foo
+
+// main is conditionally compiled, but the conditional compilation
+// is conditional too!
+
+#[cfg_attr(foo, cfg(bar))]
+fn main() { }

src/test/compile-fail/cfg-attr-crate-2.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.
+//
+// compile-flags: --cfg broken
+
+// https://github.com/rust-lang/rust/issues/21833#issuecomment-72353044
+
+#![cfg_attr(broken, no_std)] //~ ERROR no_std is experimental
+
+fn main() { }