[tlbuild] [tex-live] LuaTeX cygwin build

[Akira Kakuto]

Hi Ken,

> I did a grep of the luatex sources and found a large number of places 
> where there are special cases for Cygwin, including many where Cygwin is 
> lumped with Mingw32 and Win32.  I suspect this is what's causing the 
> problem.

Confirm that those places are not essential parts of LuaTeX.
The code only restricts output of executable files.

Best,
Akira