Xcode 7 GM presents the options to download and install all of the iOS 8.x Simulators, but when I attempt to install one of them (e.g., the iOS 8.4 Simulator), the progress bar gets to about 70% and then I get an alert panel stating "Could not download and install iOS 8.4 Simulator. Authorization is required to install the packages." However, I'm the administrator of the machine, I authenticated Xcode to "install additional components" at first boot, and I have Xcode tied to my Apple Developer account.
I've filed a bug report on this, but does anyone know how I can get Xcode to behave itself?