Summary:
see https://github.com/facebook/rocksdb/issues/7376.
The `wfe` op on ARM platform is not suitable to relax CPU. Use `yield` op.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7438

Reviewed By: riversand963

Differential Revision: D24063427

Pulled By: jay-zhuang

fbshipit-source-id: b0ebc5590d7555bd21b30f15cd59f84dc006367a