git-gui: use /cmd/git-gui.exe for shortcut

git-gui on Windows creates a shortcut that presumes the git-gui script
will run on the basic Windows environment as configured. But, Git for
Windows uses wrapper scripts to launch executables, assuring the
environment is correct (see [1] for details). The launcher for git-gui
is /cmd/git-gui.exe, is not on PATH, and is not detected or used by the
current shortcut code. Let's look for this before trying the existing
approaches.

[1] https://gitforwindows.org/git-wrapper.html

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

Author: mark987

lib/shortcut.tcl

@@ -23,7 +23,10 @@ proc do_windows_shortcut {} {
 
 	# Use git-gui.exe if found, fall back to wish + launcher
 	set link_arguments {}
-	set link_target [_which git-gui]
+	set link_target [safe_exec [list cygpath -m /cmd/git-gui.exe]]
+	if {![file executable $link_target]} {
+		set link_target [_which git-gui]
+	}
 	if {![file executable $link_target]} {
 		set link_target [file normalize [info nameofexecutable]]
 		set link_arguments [file normalize $::argv0]