[Bug java/83647] add x86_64 Windows support to GCJ

[yzhang1985 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83647

--- Comment #2 from Yale Zhang <yzhang1985 at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> GCC 6 is in regression only fixes due to it being a release branch.
> 
> Won't fix as Java was removed from GCC 7.  There are other open source Java
> implementations including but not limited to OpenJDK.

I was afraid of that, but I want to compile to native code and AFAIK, GCJ is
the only one or if not, the only robust one. I think this change can be useful
to others and shouldn't be lost just because GCC 6 is limited to regression
fixes only. Is there a non-release branch that this can checked into?