rr: enable on 32bit x86

Lack of 32bit support led to the creation
of an overlay to add it back again,
but since it at least builds and seems to work
don't see why we'd disallow it here :).

pkgs/development/tools/analysis/rr/default.nix

···
 
     license = "custom";
     maintainers = with stdenv.lib.maintainers; [ pierron thoughtpolice ];
-    platforms = ["x86_64-linux"];
+    platforms = stdenv.lib.platforms.x86;
   };
 }