MIPS32r2 doesn't have load-linked/store-conditional instructions
that work with 64-bit values and these are now implemented through
runtime.

TEST=mjsunit/wasm/compare-exchange64-stress

Change-Id: I70d8a454dcbbdac6f30e30ec3ac0eb4d429ef62e
Reviewed-on: https://chromium-review.googlesource.com/c/1296211
Commit-Queue: Ivica Bogosavljevic <ibogosavljevic@wavecomp.com>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57138}