RFR: 8272096: Exceptions::new_exception can return wrong exception [v2]

[Coleen Phillimore]

> I added an assert if Exceptions::new_exception is called with a pending exception and fixed the places where it is called with a pending exception.   That leaves only two possible exceptions. I left the product mode code in to return the pending exception if allocating the exception message doesn't thrown OOM because it was always there and seems dubious.  Tested with jck tests and tier1-7.

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

  second get_user_name_slow call should CHECK_NULL too.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9492/files
  - new: https://git.openjdk.org/jdk/pull/9492/files/d5ab48a4..daf55a4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9492&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9492&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9492.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9492/head:pull/9492

PR: https://git.openjdk.org/jdk/pull/9492