Merge https://github.com/prati0100/git-gui

* https://github.com/prati0100/git-gui: git-gui - use mkshortcut on Cygwin git-gui - use cygstart to browse on Cygwin git-gui - remove obsolete Cygwin specific code git gui Makefile - remove Cygwin modifications Makefiles: change search through $(MAKEFLAGS) for GNU make 4.4 Work around Tcl's default `PATH` lookup Move the `_which` function (almost) to the top Move is_<platform> functions to the beginning is_Cygwin: avoid `exec`ing anything windows: ignore empty `PATH` elements git-gui: Fix a typo in README