Port aa5bcc09

Original Commit Message:

    This relands commit d04b5e47.

    The fix here is in the assembler for pmovmskb, emit_optional_rex_32 should be
    called after emitting the prefix byte.

    Original change's description:
    > [wasm-simd][liftoff][ia32][x64] Implement bitmask
    >
    > Implements i8x16 i16x8 i32x4 bitmask.
    >
    > This was merged into the proposal in
    > https://github.com/WebAssembly/simd/pull/201/.
    >
    > Bug: v8:9909,v8:10308
    > Change-Id: I882f0c2697213cdf593e745112e0897cee252009
    > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2222607
    > Commit-Queue: Zhi An Ng <zhin@chromium.org>
    > Reviewed-by: Clemens Backes <clemensb@chromium.org>
    > Cr-Commit-Position: refs/heads/master@{#68090}

R=zhin@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Id73795d3628067199ac6ac592a9b0b1c57fc65a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2226311Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#68109}