rr: limit platforms to x86_64

related to #32326

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

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