Add test for compiler reexports removal

Author: GuillaumeGomez

src/test/rustdoc/no-compiler-reexport.rs

@@ -0,0 +1,7 @@
+// compile-flags: --no-defaults
+
+#![crate_name = "foo"]
+
+// @has 'foo/index.html' '//code' 'extern crate std;'
+// @!has 'foo/index.html' '//code' 'use std::prelude::v1::*;'
+pub struct Foo;