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

[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.

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

Changes: https://git.openjdk.org/jdk/pull/11059/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11059&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294947
  Stats: 23 lines in 1 file changed: 20 ins; 3 del; 0 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