Use fabs intrinsic

[workingjubilee]

I noticed there's a simd_fabs even though there is no simd_abs.
Same story as #89.

[workingjubilee]

...Why do these tests pass locally but fail on GH?

[Lokathor]

dunno but the code itself looks good.

[calebzulawski]

I just tried this on my machine (AMD) and it also passed.

[calebzulawski]

Oh wait, I rebased and ran it in release mode and it failed. Anyway, I found the problem. Look at what asm is generated for f32x4::is_infinite():

 mov     rax, rdi
 xorps   xmm0, xmm0
 movaps  xmmword, ptr, [rdi], xmm0
 ret

[workingjubilee]

wait
does that just... do nothing?

[calebzulawski]

It always returns false :)

[workingjubilee]

always finite but never normal around here, apparently. :^)

[calebzulawski]

Opened rust-lang/rust#84268 and #97.

[calebzulawski]

I posted it in the linked issue, but this looks like an LLVM 12 regression