RFR: 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes [v2]

[Daniel D.Daugherty]

> A trivial follow-up to:
> 
> JDK-8271251 JavaThread::java_suspend() fails with "fatal error: Illegal threadstate encountered: 6"
> 
> that adds a stronger sanity check of thread state when polling for safepoint/handshakes.
> 
> This fix was used to test @pchilano's fix for JDK-8271251 in my JDK17 Mach5
> Tier[1-8] runs for JDK-8271251. It has also been tested with Mach5 Tier[1-3]
> for jdk/jdk (JDK18).

Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:

  dholmes CR

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4936/files
  - new: https://git.openjdk.java.net/jdk/pull/4936/files/15167b4f..2e748859

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4936&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4936&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4936.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4936/head:pull/4936

PR: https://git.openjdk.java.net/jdk/pull/4936