RFR: 8253241: Update comment on java_suspend_self_with_safepoint_check()

[Richard Reingruber]

After JDK-8252414 the safepoint/handshake code does not take _suspend_flags into accout anymore in its assessment if a
thread is safepoint/handshake safe. This change updates the comment on
JavaThread::java_suspend_self_with_safepoint_check().

I have (not yet) fixed the line breaks (fill-paragraph in emacs lingo) for a clearer diff.

Also I could inline the (*) footnote.

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Commit messages:
 - 8253241: Update comment on java_suspend_self_with_safepoint_check()

Changes: https://git.openjdk.java.net/jdk/pull/225/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=225&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253241
  Stats: 8 lines in 1 file changed: 2 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/225.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/225/head:pull/225

PR: https://git.openjdk.java.net/jdk/pull/225