This allows us to reuse this optimized code sequence in Liftoff.

We can't do the same thing in IA32 yet, there is no kScratchDoubleReg
defined in the macro-assembler-ia32.cc, it is defined in code-generator-ia32
as xmm0 but I'm not sure if it is safe to just use that in the macro assembler.

Change-Id: I6c761857c49d2518fbc82cd0796c62fc86665cb5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2596581
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71915}