changes requesting for GCC 17 Release Criteria (secondary targets)

Hi all,
  I would like to request some changes to the secondary tasrgets of
the GCC 17 Release Criteria. As the secondary targets seem out of date
in some cases.

I propose to switch out mips64-linux-gnu with riscv64-linux-gnu as
being a secondary platform. riscv64-linux-gnu is gaining in popularity
and is riscv backend is actively maintained. There is much less
hardware available for mips64 too. Note we should maybe even consider
riscv64-linux-gnu for primary with GCC 18 but that might be too soon
at this point.

Also `i686-mingw32` should be swapped out with `x86_64-mingw`. I don't
think 32bit mingw is being testing these days only 64bit.
Also I propose removing `i686-pc-cygwin`, I have not seen any recent
work on 32bit x86 cygwin or testresults.
Note I think adding `aarch64-mingw` would be too soon to add at this
stage. Though I think we should reconsider it for GCC 18.

So the full for the secondary targets which I am proposing:
aarch64-elf
i686-apple-darwin
x86_64-mingw32
s390x-linux-gnu
riscv64-linux-gnu


Thanks,
Andrew