New Port for RISC-V v3

[Palmer Dabbelt <palmer at dabbelt dot com>]

There have been a handful of changes since we submitted our v2 port:

 * Some documentation formatting fixes.

 * A documentation typo fix.

 * Some changes to wwwdocs, which have been mailed to the list.

 * The port now builds via contrib/config-list.mk.  I worked around the
   warnings in other parts of the codebase with some "#pragma GCC diagnostic
   ignored" when I couldn't fix them properly, so the patches aren't useful,
   but I fixed the warnings in our port reasonably.  I can try to fix all these
   reasonably, but it might take a while.

As far as I know there are currently no outstanding problems with this port, so
I think it's at the point where we should talk about actually getting the code
in.  We have been accepted as maintainers of the port, and I have write access
to the repositories, so I think we're all good to go on that end.  Of course if
there's any remaining comments I'd love to fix them, but it seems the comments
on our v2 were somewhat minimal.

What's the procedure for moving forward with the port?

Thanks to everyone who helped with reviewing the port!

[PATCH 1/6] RISC-V Port: gcc/config/riscv/riscv.c
[PATCH 2/6] RISC-V Port: gcc
[PATCH 3/6] RISC-V Port: libgcc
[PATCH 4/6] RISC-V Port: libatomic
[PATCH 5/6] RISC-V Port: gcc/testsuite
[PATCH 6/6] RISC-V Port: contrib