I understand this is an xcode warning/error, however, it happens when I try to run gitk --all from the command line.
gitk --all
YuFei-Zhus-MacBook-Pro:test phi
On Mountain Lion 10.8.2, I fixed this issue installing/upgrading tcl and tk – as tair mentioned.
brew install tcl brew install tk
The UI of gitk will likely change, but you can tweak that in ~/.gitk.