select, {eq,lt,gt}_i32 on x86

Add vpblendvb, vpcmpeqd, and vpcmpgtd, to implement select and eq/lt/gt.
I want to think just a touch bit more about neq, lte, and gte.

This is enough to JIT everything SkVMBlitter creates today.

There are 24 possible argument orders to vpblendvb,
so I'm sure I've got them wrong somehow, even with the new test.

Change-Id: I357664b866d8258a2b5438d520f47542ad581c50
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232060
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed