RFR: JDK-8294947: Use 64bit atomics in patch_verified_entry on x86_64 [v2]

[Dmitry Samersoff]

> In the void NativeJump::patch_verified_entry() we atomically patch first 4 bytes, then atomically patch 5th byte, then atomically patch first 4 bytes again. But from CMC (cross-modified code) point of view it's better to patch atomically 8 bytes at once.
> 
> The patch was tested with hotspot jtreg tests in bare-metal and virtualized environments.

Dmitry Samersoff has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8294947: Use 64bit atomics in patch_verified_entry on x86_64

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11059/files
  - new: https://git.openjdk.org/jdk/pull/11059/files/198a1e85..bbacb7f4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11059&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11059&range=00-01

  Stats: 13 lines in 1 file changed: 3 ins; 4 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/11059.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11059/head:pull/11059

PR: https://git.openjdk.org/jdk/pull/11059