git: openjdk/jdk-sandbox: riscv-port-branch: Add comments for code changes in files os.cpp and os_posix.cpp

[duke]

Changeset: 39e0f6ca
Author:    Fei Yang <felix.yang at huawei.com>
Date:      2021-10-23 07:47:29 +0000
URL:       https://git.openjdk.java.net/jdk-sandbox/commit/39e0f6ca5a95774a57c9e07930015698e0530b29

Add comments for code changes in files os.cpp and os_posix.cpp

! src/hotspot/os/posix/os_posix.cpp
! src/hotspot/share/opto/memnode.hpp
! src/hotspot/share/runtime/os.cpp