Broken bootstrap on Cygwin

[FX]

> GCC maintainers is this OK for your policy?

Personally, I don't think it's a good thing to do: a secondary platform that only supports the latest released version of said platform does not indicate high stability. But it's up to the cygwin maintainers to decide, of course.

However, the fact should be documented on the installation notes (http://gcc.gnu.org/install/specific.html#x-x-cygwin) and probably on the release notes as well, with something like "The GCC 4.6 series requires Cygwin x.y.z or later".

FX