The problem occurs when getting an unused register causes spilling, but
the generated code is not executed because of a branch, resulting in
loss of data.

BUG=
TEST=cctest/test-run-wasm/RunWasmLiftoff_I64Sh*

Change-Id: Icdb897df42059ed27bec57fcf91cc8338e4598f3
Reviewed-on: https://chromium-review.googlesource.com/1060213Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#53200}