RFR: 8254264: Remove redundant cross_modify_fence()

[Patricio Chilano Mateo]

Hi all,

Please review the following patch that removes some uneeded uses of cross_modify_fence() in common code, in particular
from ~ThreadBlockInVM(), ~ThreadBlockInVMWithDeadlockCheck() and java_suspend_self_with_safepoint_check(). These fences
were added before each JavaThread had to disarm itself (8230594). After a safepoint/handshake each JavaThread will
always call SafepointMechanism::process_if_requested_slow() when transitioning out of the safe state and will execute a
cross_modify_fence(). Tested with mach5 tiers1-7.

Thanks,
Patricio

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Commit messages:
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/655/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=655&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254264
  Stats: 5 lines in 2 files changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/655.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/655/head:pull/655

PR: https://git.openjdk.java.net/jdk/pull/655