/usr/share/zsh/5.5.1/functions
Edit: /usr/share/zsh/5.5.1/functions/VCS_INFO_check_com (294B)
## vim:ft=zsh
## Written by Frank Terbeck
## Distributed under the same BSD-ish license as zsh itself.
setopt localoptions NO_shwordsplit
case $1 in
(/*)
[[ -x $1 ]] && return 0
;;
(*)
(( ${+commands[$1]} )) && return 0
esac
return 1