w64devkit.exe: Support for "-c" and/or "--" to pass args through to busybox sh

After all the floundering in #199, the most straight forward solution seems to be as you described. I keep coming back and wanting this. Would you be open to implement this feature?

You see I have this nice logo that shows when I open the shell:

w64devkit [Version 2.1.0]
by skeeto (Christopher Wellons). Unlicense.

C:/Users/stian>

I made that logo when I first started out with w64devkit to add some familiarity from good old cmd.exe:

Microsoft Windows [Version 10.0.26100.4946]
(c) Microsoft Corporation. All rights reserved.

C:\Users\stian>

It's just a cute thing and I really like it. It was the first thing I did. Other than the familiarity I also like that it advertises your project when I'm streaming and coding.

But whenever I spawn shells through Windows' graphical shell (like Open in Terminal or my own Edit in Terminal), I can't use w64devkit.exe (as thoroughly explored in #199), so my logo gets all messed up, since it's lacking $W64DEVKIT & $W64DEVKIT_HOME:

(Yes, I added red standout for dramatic effect.)

I also use $W64DEVKIT_HOME for managing w64devkit's tags file, which goes out the window when I spawn a shell this way.

Anyway :) If it's not counter to your desired design, please consider adding this functionality!

Start with w64devkit.exe's command-line handling and the linked discussion in issue #199, then trace how arguments reach BusyBox sh. Define the behavior for -c and/or --, including pass-through arguments, and verify that launching from Windows graphical shells preserves the expected environment and prompt behavior.