Auto merge of #53893 - petrochenkov:cfgexpr, r=pnkfelix

Validate syntax of `cfg` attributes

Fixes https://github.com/rust-lang/rust/issues/53298

src/test/ui/issues/issue-31495.rs

@@ -1,13 +0,0 @@
-// 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 foo(bar)
-// error-pattern: invalid predicate in --cfg command line argument: `foo`
-fn main() {}