Unordered floating-point (non-)equality is implemented using two flags
on x64: kUnorderedNotEqual as "not_equal OR parity_even" and
kUnorderedEqual as "equal AND parity_odd". Only the first flag was
checked.

This change fixes the kUnorderedNotEqual case by emitting a second
cmov to also move the "true" value if the parity_even flag is set. The
kUnorderedEqual case is covered by inverting the condition in the
instruction selector.

This should also be optimal according to the code emitted by clang -O3
for equivalent C++ code.

Drive-by: remove unused overload of EmitWithContinuation.

R=neis@chromium.org
CC=ahaas@chromium.org

Bug: chromium:1200184
Change-Id: Iae438d29fb5897ca910a154f140a5a6a904490ec
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2844651
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74122}