simd: implement missing intrinsics from simd/generic-arithmetic-pass.rs

[sadlerap]

This implements/fixes the following intrinsics:

• simd_bswap
• simd_frem
• simd_bitreverse
• simd_ctlz
• simd_cttz
• simd_neg

These were the remaining intrinsics from the simd/generic-arithmetic-pass.rs ui test, which should now pass for a patched libgccjit. However, it seems not to compile against a non-patched libgccjit, so leave it disabled there for now.

[antoyo]

I'll do the review soon, hopefully in the next few days. I've been quite busy lately.

[sadlerap]

No worries, take all the time you need.

[sadlerap]

Apologies on the delay on getting back to your review - last week's holidays made things busy for me, and I couldn't get back to this until now.

[antoyo]

Thanks a lot for your contribution!