The codegen uses a bunch of vpmax to try and keep set bits around. The
datatype for vpmax does not need to change for each instruction, since
vpmax U32 will persist set bits just as well. This simplifies the
instruction sequences for S1x8 and S1x16 anytrue.

I added a test to check a special case when a f64x2 contains -0.0 (top
bit set). A previous attempt to optimize codegen used floating point
compare, which does not distinguish between 0.0 and -0.0. So -0.0 will
compare equals to 0.0, and incorrect return 0 for anytrue.

Change-Id: I66013796af08a666009e6b2d774ea7ee7bdfe1ad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2203113
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67875}