RFR: 8275917: Some locks shouldn't allow_vm_block

[Coleen Phillimore]

There were a few safepoint checking locks that passed allow_vm_block as true, that aren't taken by the VMThread.  I also made ClassInitError_lock behave like SystemDictionaryLock and the others in SystemDictionary::do_unloading so that doesn't require allow_vm_block either.  See the CR for more details.

Tested with tier1-6.

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Commit messages:
 - 8275917: Some locks shouldn't allow_vm_block

Changes: https://git.openjdk.java.net/jdk/pull/6123/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6123&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275917
  Stats: 23 lines in 3 files changed: 1 ins; 0 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6123.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6123/head:pull/6123

PR: https://git.openjdk.java.net/jdk/pull/6123