Merge branch 'cb/no-tcl86-on-macos'

* cb/no-tcl86-on-macos: git-gui: ensure own version of git-gui--askpass is used git-gui: honor TCLTK_PATH in git-gui--askpass git-gui: retire Git Gui.app git-gui: fix dependency of GITGUI_MAIN on generator git-gui: remove uname_O in Makefile