RFR: 8290324: Move atomic operations outside of os_xxx.hpp [v4]

[Ioi Lam]

> The os_xxx.hpp files inject extra methods/fields that are specific to atomic operations into the `os` class. However, the injected methods/fields are used only by a specific os/cpu combination. Therefore, they should not be inside the `os` class, which should contain only APIs that are used across platforms.
> 
> - For ports where the `atomic_copy64()` function is used in a single file, I moved it as an inline function in that file
> - Otherwise it's moved to `atomic_<os>_<cpu>.hpp`
> - The linux/arm port is a little more involved, but the new code should be a little cleaner than the old code.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  moved 'static inline void atomic_copy64' outside of 'extern "C"' block

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9501/files
  - new: https://git.openjdk.org/jdk/pull/9501/files/397ba800..0d8a150f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9501&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9501&range=02-03

  Stats: 24 lines in 3 files changed: 12 ins; 12 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9501.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9501/head:pull/9501

PR: https://git.openjdk.org/jdk/pull/9501