Rollup merge of #52385 - GuillaumeGomez:pass-edition-to-parser, r=QuietMisdreavus

Pass edition flags to compiler from rustdoc as expected

Fixes #52357.

src/test/rustdoc/edition-flag.rs

@@ -0,0 +1,24 @@
+// Copyright 2018 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 -Z unstable-options
+// edition:2018
+
+#![feature(async_await)]
+
+/// ```rust
+/// #![feature(async_await)]
+/// fn main() {
+///     let _ = async { };
+/// }
+/// ```
+fn main() {
+    let _ = async { };
+}