Add support for LoongArch64

[heiher]

Follow up #1565

[briansmith]

@heiher The stuff in base.h is now to be in target.h. Note that the clippy job failed; try mk/clippy.sh. Please rebase on the main branch and resubmit.

[briansmith]

Is there no QEMU support for this target? Could you please add the rest of the stuff like the other targets have for QEMU to cargo.sh and install-build-tools.sh? This makes it very easy for us to all test this target manually, even if we don't add it to CI.

[codecov]

Codecov Report

Merging #1632 (78a453f) into main (901441f) will decrease coverage by 0.01%.
Report is 5 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1632      +/-   ##
==========================================
- Coverage   96.04%   96.03%   -0.01%     
==========================================
  Files         133      133              
  Lines       19913    19913              
  Branches      199      199              
==========================================
- Hits        19125    19124       -1     
  Misses        752      752              
- Partials       36       37       +1     

see 1 file with indirect coverage changes

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[briansmith]

I couldn't find the toolchain support in Ubuntu 22.04. Please help Ubuntu get your cross-compilation and QEMU support into Ubuntu if you haven't already. Thanks!

[heiher]

I couldn't find the toolchain support in Ubuntu 22.04. Please help Ubuntu get your cross-compilation and QEMU support into Ubuntu if you haven't already. Thanks!

You're right. Fortunately, Debian/LoongArch port is already in progress. Thanks!