RFR: JDK-8258479: Minor cleanups in VMError [v3]

[Thomas Stuefe]

> A list of smaller cleanups, each one too small to justify an own issue:
> 
> 1) VMError exposes is_error_reported(), fatal_error_in_progress() and get_first_error_tid(). These functions are used from outside to check on the state of error handling. They can be combined and duplicate coding removed. Also, VMError::_error_reported can be removed, since its redundant with VMError::_first_error_tid != -1)
> 2) A lot of methods are unnecessarily public
> 3) the `env_var` array in vmError.cpp can be limited to file scope
> 4) definition of VMError static members should be combined to the start of the cpp file
> 5) the comment describing VMError::report() is misplaced
> 6) VMError::reset_signal_handlers() is badly named; nothing is reset here, the secondary signal handler is installed.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  Fix Copyrights

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1802/files
  - new: https://git.openjdk.java.net/jdk/pull/1802/files/47c59b57..b286e94c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1802&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1802&range=01-02

  Stats: 7 lines in 6 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1802.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1802/head:pull/1802

PR: https://git.openjdk.java.net/jdk/pull/1802