Fixed compile warning (#774)

* Fixed compile warning

* Better fix for compile warning

Author: UebelAndre

test/unit/cc_info/cc_info_test.bzl

@@ -102,6 +102,7 @@ def _cc_info_test():
         name = "proc_macro",
         srcs = ["proc_macro.rs"],
         edition = "2018",
+        deps = ["//test/unit/native_deps:native_dep"],
     )
 
     rlib_provides_cc_info_test(

test/unit/cc_info/proc_macro.rs

@@ -3,7 +3,9 @@ use proc_macro::TokenStream;
 extern "C" {
     fn native_dep() -> isize;
 }
+
 #[proc_macro_derive(UsingNativeDep)]
-pub fn use_native_dep(_input: TokenStream) -> TokenStream {
-    panic!("done")
+pub fn use_native_dep(input: TokenStream) -> TokenStream {
+    println!("{}", unsafe { native_dep() });
+    input
 }

test/unit/native_deps/native_deps_test.bzl

@@ -187,6 +187,7 @@ def _native_dep_test():
     cc_library(
         name = "native_dep",
         srcs = ["native_dep.cc"],
+        visibility = ["//test/unit:__subpackages__"],
     )
 
     cc_library(