If we have both f32 and f64 locals, we use the same register to hold
their zero value. On stack transfers, we might thus encounter the same
fp register with both the f32 and f64 type. Explicitly allow that case
to happen.

R=ahaas@chromium.org

Bug: chromium:918917, v8:6600
Change-Id: I6937008d38853fe2bdccd9715e1a2499cf6bf7c6
Reviewed-on: https://chromium-review.googlesource.com/c/1398225Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58623}