[tlbuild] Build progress with CYGWIN

[Akira Kakuto]

>     1- (Solved) Because Windows does not distinguish uppercase from
>        lowercase file names there was a confusion between a system
>        /usr/include/features.h file and a .../libs/icu-xetex/layout/Features.h
> 
> But shouldn't the -I options find the icu-xetex file first in any case?
> I don't recall Akira ever mentioning this problem on Windows, but maybe
> he just silently solved it ... Akira?

I didn't have this problem.
BTW, there is no features.h in system headers of MSVC++, which
I'm using to build xetex.

Best,
Akira