Removal of support for GCC hosted on UWIN

[Joe Buck]

> Is not U/Win in the same category as CygWin ?  Or DJGPP for that matter ?

With CygWin and DJGPP, the linked-to libraries are free software.  With
U/Win, the linked-to library is proprietary, but is not (to quote the GPL)
"normally distributed (in either source or binary form) with the major
components (compiler, kernel, and so on) of the operating system on which
the executable runs ...".  That's the difference.