treewide: Add lots of platforms to packages with no meta

Build-tested on x86_64 Linux and on Darwin.

pkgs/development/libraries/java/smack/default.nix

@@ -8,4 +8,8 @@ stdenv.mkDerivation {
     url = http://www.igniterealtime.org/downloadServlet?filename=smack/smack_3_4_1.tar.gz;
     sha256 = "13jm93b0dsfxr62brq1hagi9fqk7ip3pi80svq10zh5kcpk77jf4";
   };
+
+  meta = {
+    platforms = stdenv.lib.platforms.unix;
+  };
 }