Another issue after installing the El Capitan beta yesterday: Emacs became slow and had font issues. Recording my fix here for future reference.

Upgraded to Xcode 7 beta and installed the latest command line tools

The beta application is named “Xcode beta” so I deleted the original and told the system to use the new one. Updated the app using homebrew and emacs was back in action.

sudo xcode-select --switch /Applications/Xcode-beta.app
brew update
brew upgrade emacs-mac
brew linkapps emacs-mac