Some Linux kernels are built without `madvise()`. In that
case, do not crash but rather ignore the return value instead.

Refs: https://github.com/nodejs/node/issues/21562
Change-Id: Iff8d0d0e9e7935804e2fc994be7f8bd21c553846
Reviewed-on: https://chromium-review.googlesource.com/1131943Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54415}