c-ares: add downstream tests

pkgs/development/libraries/c-ares/default.nix

@@ -1,6 +1,10 @@
 { lib, stdenv, fetchurl, writeTextDir
 , fetchpatch
 , withCMake ? true, cmake
+
+# sensitive downstream packages
+, curl
+, grpc # consumes cmake config
 }:
 
 # Note: this package is used for bootstrapping fetchurl, and thus
@@ -31,6 +35,10 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  passthru.tests = {
+    inherit curl grpc;
+  };
+
   meta = with lib; {
     description = "A C library for asynchronous DNS requests";
     homepage = "https://c-ares.haxx.se";