Add a test for rust-lang#38273

Closes 38273

Author: nrc

src/test/compile-fail/rmeta-priv-warn.rs

@@ -0,0 +1,21 @@
+// 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: --emit=metadata
+// no-prefer-dynamic
+// must-compile-successfully
+
+#[deny(warnings)]
+
+// Test that we don't get warnings for non-pub main when only emitting metadata.
+// (#38273)
+
+fn main() {
+}