RFR: 8265932: Move safepoint related fields from class Thread to JavaThread

[Patricio Chilano Mateo]

Hi,

Please review the following change. A left over from 8265453 was moving _poll_data from class Thread to JavaThread. There are also other fields like _no_safepoint_count and _visited_for_critical_count that should be moved.
Tested in mach5 tiers 1-5. Tested it builds ppc, arm and s390. Tested it builds in release, optimized and fastdebug modes.

Thanks,
Patricio

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Commit messages:
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/3695/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3695&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265932
  Stats: 239 lines in 30 files changed: 90 ins; 99 del; 50 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3695.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3695/head:pull/3695

PR: https://git.openjdk.java.net/jdk/pull/3695