Allow extern statics with an extern type

Fixes #55239

src/test/ui/static/static-extern-type.rs

@@ -0,0 +1,37 @@
+// 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-pass
+#![feature(extern_types)]
+
+pub mod a {
+    extern "C" {
+        pub type StartFn;
+        pub static start: StartFn;
+    }
+}
+
+pub mod b {
+    #[repr(transparent)]
+    pub struct TransparentType(::a::StartFn);
+    extern "C" {
+        pub static start: TransparentType;
+    }
+}
+
+pub mod c {
+    #[repr(C)]
+    pub struct CType(u32, ::b::TransparentType);
+    extern "C" {
+        pub static start: CType;
+    }
+}
+
+fn main() {}