Testing 64-bit RISC-V support

[W. J. van der Laan]

> > Required patches for M1 and hex2_linker can be found at
> > https://github.com/laanwj/guix-mescc-tools/commits/riscv . I will upstream
> > these to mescc-tools separately.
>
> Okay, great. I'll probably add a temporary commit for that to setup an
> environment. Have you tried running it with qemu emulation support? We
> tried that for ARM with mixed results...

This is a great idea, it seems to work on Debian at least; I set up a riscv64 
chroot using debootstrap and qemu-user:

================================================================================
apt install debootstrap qemu-user-static binfmt-support 
debian-ports-archive-keyring
debootstrap --arch=riscv64 --keyring 
/usr/share/keyrings/debian-ports-archive-keyring.gpg 
--include=debian-ports-archive-keyring unstable /tmp/riscv64-chroot 
http://deb.debian.org/debian-ports
chroot /tmp/riscv64-chroot
================================================================================

Then install the packages and everything
================================================================================
apt install binutils git make gcc nyacc guile-3.0-dev
git clone https://github.com/laanwj/guix-mes.git
git clone --recurse-submodules https://github.com/laanwj/guix-mescc-tools
cd guix-mescc-tools
make
cd ..
export PATH="/root/guix-mescc-tools/bin:$PATH"
cd guix-mes
./configure --with-bootstrap
make
================================================================================

This worked here to get a bin/mes-gcc and bin/mes-mescc
A full qemu-system should be even more "realistic" but will likely be 
noticeably slower.

-W