Rollup merge of rust-lang#34969 - jseyfried:fix_cfg_feature, r=nrc

Avoid processing `feature`s on unconfigured crates

Fixes rust-lang#34932, a regression caused by rust-lang#34272.
r? @nrc

src/libsyntax/config.rs

@@ -124,7 +124,7 @@ pub fn strip_unconfigured_items(mut krate: ast::Crate, sess: &ParseSess, should_
         };
 
         let err_count = sess.span_diagnostic.err_count();
-        let krate_attrs = strip_unconfigured.process_cfg_attrs(krate.attrs.clone());
+        let krate_attrs = strip_unconfigured.configure(krate.attrs.clone()).unwrap_or_default();
         features = get_features(&sess.span_diagnostic, &krate_attrs);
         if err_count < sess.span_diagnostic.err_count() {
             krate.attrs = krate_attrs.clone(); // Avoid reconfiguring malformed `cfg_attr`s

src/test/run-pass/issue-34932.rs

@@ -0,0 +1,23 @@
+// Copyright 2016 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:--test
+// rustc-env:RUSTC_BOOTSTRAP_KEY=
+// ignore-pretty : (#23623) problems when  ending with // comments
+
+#![cfg(any())] // This test should be configured away
+#![feature(rustc_attrs)] // Test that this is allowed on stable/beta
+#![feature(iter_arith_traits)] // Test that this is not unused
+#![deny(unused_features)]
+
+#[test]
+fn dummy() {
+    let () = "this should not reach type-checking";
+}