Stop `make` if working tree does not have git repository (#263)
Stop `make` if working tree does not have git repository (#263)

Fix https://github.com/jpsim/SourceKitten/issues/262
See also: https://github.com/jspahrsummers/objc-build-scripts/issues/13
jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten