Feature gate macro arguments

Uses the same approach as https://github.com/rust-lang/rust/pull/17286 (and
subsequent changes making it more correct), where the visitor will skip any
pieces of the AST that are from "foreign code", where the spans don't line up,
indicating that that piece of code is due to a macro expansion.

If this breaks your code, read the error message to determine which feature
gate you should add to your crate, and bask in the knowledge that your code
won't mysteriously break should you try to use the 1.0 release.

Closes #18102

[breaking-change]

src/test/compile-fail/feature-gated-feature-in-macro-arg.rs

@@ -0,0 +1,24 @@
+// Copyright 2014 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.
+
+// tests that input to a macro is checked for use of gated features. If this
+// test succeeds due to the acceptance of a feature, pick a new feature to
+// test. Not ideal, but oh well :(
+
+fn main() {
+    let a = &[1i32, 2, 3];
+    println!("{}", {
+        extern "rust-intrinsic" { //~ ERROR intrinsics are subject to change
+            fn atomic_fence();
+        }
+        atomic_fence();
+        42
+    });
+}