RFR: 8275917: Some locks shouldn't allow_vm_block [v2]

[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.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Remove incorrect comment.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6123/files
  - new: https://git.openjdk.java.net/jdk/pull/6123/files/767ff817..aa68f26d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6123&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6123&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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