gecode: re-enable gecode gist
gecode: re-enable gecode gist

The possibility to use gecode gist was removed with the removal of the
qt option in 67cbc222f67ec7c480efc9cc3209ddf88922a056.

adam-moss/homebrew-core,nandub/homebrew-core,zyedidia/homebrew-core,sjackman/homebrew-core,mfikes/homebrew-core,makigumo/homebrew-core,nbari/homebrew-core,lemzwerg/homebrew-core,nandub/homebrew-core,sjackman/homebrew-core,zyedidia/homebrew-core,chrisfinazzo/homebrew-core,filcab/homebrew-core,nbari/homebrew-core,mfikes/homebrew-core,uyjulian/homebrew-core,cblecker/homebrew-core,stgraber/homebrew-core,cblecker/homebrew-core,chrisfinazzo/homebrew-core,uyjulian/homebrew-core,lemzwerg/homebrew-core,filcab/homebrew-core,adam-moss/homebrew-core,makigumo/homebrew-core,Homebrew/homebrew-core,stgraber/homebrew-core,Homebrew/homebrew-core