Merge branch 'pks-meson-support' of github.com:pks-t/git-gui

Merge branch 'pks-meson-support' of github.com:pks-t/git-gui

* 'pks-meson-support' of github.com:pks-t/git-gui:
  git-gui: wire up support for the Meson build system
  git-gui: stop including GIT-VERSION-FILE file
  git-gui: extract script to generate macOS app
  git-gui: extract script to generate macOS wrapper
  git-gui: extract script to generate "tclIndex"
  git-gui: extract script to generate "git-gui"
  git-gui: drop no-op GITGUI_SCRIPT replacement
  git-gui: make output of GIT-VERSION-GEN source'able
  git-gui: prepare GIT-VERSION-GEN for out-of-tree builds
  git-gui: replace GIT-GUI-VARS with GIT-GUI-BUILD-OPTIONS

Signed-off-by: Johannes Sixt <j6t@kdbg.org>