Changes checked in to allow building with gcc4.x

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

I have just checked in changes which should allow Cygwin to build with a
recent gcc-4.x compiler without the need for the -mno-cygwin option.

I did this by creating a mingw gcc front-end script which massages the
options that it receives, removing cygwin-specific ones, and adding
appropriate pointers to installed mingw locations.  This adds options
which point to usr/i686-pc-mingw32 as appropriate.  I don't know if
Cygwin will build without all of the files that come with gcc-mingw or
not.  I didn't check this but it would have been interesting to do a
before/after comparison.

The latest snapshot has been built with a linux cross-compiler created
from Dave Korn's latest compiler + some patches required to get things
building as a cross-compiler.  I've also built cygwin on Windows to
verify that the front-end script works there.  It does, with the usual
depressing slowness of a cygwin shell script.

The mingw front-end script is crude and makes assumptions that are
particular to building in the winsup/...  directory.  It would probably
not be usable as a general-purpose mingw front end.  I also surely would
not want to support it in that capacity.

FYI.

cgf