Add LoongArch SIMD intrinsics

[heiher]

This PR adds LoongArch SIMD (LSX/LASX) intrinsics and testcases.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Amanieu (or someone else) some time within the next two weeks.

[Amanieu]

Are the tests also automatically generated, or just the intrinsic definitions?

[heiher]

Are the tests also automatically generated, or just the intrinsic definitions?

The tests are also automatically generated, but not by this generator.

[Amanieu]

Can you also include the generator used for making the tests? I don't want to include any auto-generated code in this repo without also including the generator used to create it.

Finally, can you also commit a copy of the header files used to generate the .spec files?

[heiher]

Can you also include the generator used for making the tests? I don't want to include any auto-generated code in this repo without also including the generator used to create it.

Finally, can you also commit a copy of the header files used to generate the .spec files?

Thanks for your review. I have updated the patch to include code for generating test cases and also added copying of header files.

[Amanieu]

This looks great! Just a few minor changes and this is good to merge.