MIPS architecture doesn't have support for 64-bit atomics.
It is possible to implement them using 32-bit atomics,
but the process is involved and takes time. For the time
being support 64-bit atomics using runtime.

Bug: v8:8100
Change-Id: I8c732ea9975c46be70643a1e722d78938c8a70de
Reviewed-on: https://chromium-review.googlesource.com/1251521
Commit-Queue: Ivica Bogosavljevic <ibogosavljevic@wavecomp.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56331}