LoongArch64 Support

[maoif]

This pull request adds support for LoongArch64, which is an ISA similar to RISC-V.
The machine type as returned by (machine-type) is [t]la64le, the internal architecture name is loongarch64.

This PR is basically an adaptation of this old PR toward those
new features like unboxed floating points and vfasl.

[mflatt]

This is very nicely done! I built (in a qemu-hosted Arch Linux installation) and ran make test-one with no issues. I would like to test a little more, but this looks ready to go. Assuming it's ok, I would rebase, drop the merge commit, and fix the conflict in configure that I recently introduced before trying to merge the PR.

[maoif]

This is very nicely done! I built (in a qemu-hosted Arch Linux installation) and ran make test-one with no issues. I would like to test a little more, but this looks ready to go. Assuming it's ok, I would rebase, drop the merge commit, and fix the conflict in configure that I recently introduced before trying to merge the PR.

Thanks.

BTW, I ran the VM using the image here (in my case only 20.3 and 20.4 can boot) and the EFI file here:

qemu-system-loongarch64 \
          -m 8G -M virt -smp 4 \
          -cpu la464-loongarch-cpu \
          -serial stdio \
          -bios QEMU_EFI_8.1.fd \
          -device virtio-gpu-pci \
          -device nec-usb-xhci,id=xhci,addr=0x1b \
          -device usb-tablet,id=tablet,bus=xhci.0,port=1 \
          -device usb-kbd,id=keyboard,bus=xhci.0,port=2 \
          -net nic -net user \
          -nic user,hostfwd=tcp::33334-:22 \
          -hda Loongnix-20.4.cartoon.mini.loongarch64.cn.qcow2

Initial user:password: loongson:Loongson20

Aside from that, maybe we can add some github actions using this project to automate test for non-x86 architectures.
It doesn't support loongarch now so more work needs to be done.

However, I tried using this project on my local branch a while ago and had some test failures that did not
appear when run on qemu and the test time was several times longer.

[mflatt]

As an extra check, I built on hardware provided by Loongson at https://portal.cfarm.net/, which is about twice as fast a qemu on my machine, and ran more tests there. I found a failure that happens when running 5_6.ms with cp0=t, which is easiest to see this way:

cd tla64le/mats
../../bin/zuo . 5_6.mo cp0=t
grep compiler-internal 5_6.mo

shows

Expected error in mat vector-cas!: "compiler-internal: cas: no match found for (#{t d9q40fxqwbl62hchjs8tny84i-0} zero #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 536870921] #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 16] #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 24])".
Expected error in mat vector-cas!: "compiler-internal: cas: no match found for (#{t d9q40fxqwbl62hchjs8tny84i-1} zero #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 8796093022217] #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 16] #[#{L15c:Triv:immediate jczowy6yjfz400ntojb6av7y0-15c-36} 36 24])".

where the expected errors are

Expected error in mat vector-cas!: "vector-cas!: 67108864 is not a valid index for #(4 5 3)".
Expected error in mat vector-cas!: "vector-cas!: 1099511627776 is not a valid index for #(4 5 3)".

[mflatt]

Interestingly, but maybe not surprisingly, trv64le fails on the same way with that test+configuration.

[maoif]

The "compiler-internal" error is fixed in the new commit.

[mflatt]

Thanks!