Removal of support for GCC hosted on UWIN

[dewar@gnat.com]

<<However, Interix is not normally distributed with the NT kernel.  So
it doesn't matter whether you consider the kernel to be the OS, or
Interix to be the OS, because you don't get both of them together than
you can't link a GPLed program with them and distribute it.
>>

To emphasize this further. OpenVMS is not normally distributed with
Tru64, but this does not mean that OpenVMS is therefore somehow in
the same category as third party software not covered by the exception.

The exception clause is with respect to an operating system, it is talking
about things athat are normally distributed with the operating system.

Interix *IS* an operating system, so the issue of the exception clause is
with respect to what components are normally distributed with Interix.