made the pack completely portable and wrote relevent bat files to go with it

gitportable/mingw64/libexec/git-core/git-gui--askpass

@@ -0,0 +1,84 @@
+#!/bin/sh
+# Tcl ignores the next line -*- tcl -*- \
+exec wish "$0" -- "$@"
+
+# This is a trivial implementation of an SSH_ASKPASS handler.
+# Git-gui uses this script if none are already configured.
+
+package require Tk
+
+set answer {}
+set yesno  0
+set rc     255
+
+if {$argc < 1} {
+	set prompt "Enter your OpenSSH passphrase:"
+} else {
+	set prompt [join $argv " "]
+	if {[regexp -nocase {\(yes\/no\)\?\s*$} $prompt]} {
+		set yesno 1
+	}
+}
+
+message .m -text $prompt -justify center -aspect 4000
+pack .m -side top -fill x -padx 20 -pady 20 -expand 1
+
+entry .e -textvariable answer -width 50
+pack .e -side top -fill x -padx 10 -pady 10
+
+proc on_show_input_changed {args} {
+	global show_input
+	if {$show_input} {
+		.e configure -show ""
+	} else {
+		.e configure -show "*"
+	}
+}
+trace add variable show_input write "on_show_input_changed"
+
+set show_input 0
+
+if {!$yesno} {
+	checkbutton .cb_show -text "Show input" -variable show_input
+	pack .cb_show -side top -anchor nw
+}
+
+frame .b
+button .b.ok     -text OK     -command finish
+button .b.cancel -text Cancel -command cancel
+
+pack .b.ok -side left -expand 1
+pack .b.cancel -side right -expand 1
+pack .b -side bottom -fill x -padx 10 -pady 10
+
+bind . <Visibility> {focus -force .e}
+bind . <Key-Return> [list .b.ok invoke]
+bind . <Key-Escape> [list .b.cancel invoke]
+bind . <Destroy>    {set rc $rc}
+
+proc cancel {} {
+	set ::rc 255
+}
+
+proc finish {} {
+	if {$::yesno} {
+		if {$::answer ne "yes" && $::answer ne "no"} {
+			tk_messageBox -icon error -title "Error" -type ok \
+				-message "Only 'yes' or 'no' input allowed."
+			return
+		}
+	}
+
+	# On Windows, force the encoding to UTF-8: it is what `git.exe` expects
+	if {$::tcl_platform(platform) eq {windows}} {
+		set ::answer [encoding convertto utf-8 $::answer]
+	}
+
+	puts $::answer
+	set ::rc 0
+}
+
+wm title . "OpenSSH"
+tk::PlaceWindow .
+vwait rc
+exit $rc