RFR: 8285792: Posix signal handler modification checking issues.

[Harold Seigel]

Please review this fix for JDK-8285792.  The fix removes print statements from check_signal_handler() so that it doesn't print all the handlers every time it finds one that is modified.  Instead, it returns true if the handler is modified, false otherwise.  Its caller, user_handler(), then prints all the handlers just once even if multiple signal handlers were modified.

The fix also adds a check for VMError::crash_handler_adress() to check_signal_handler() to prevent it from being treated as a signal handler modification.

The fix was tested with Mach5 tiers 1-2 on Linux and Mac OS and Mach 5 tiers 3-5 on Linux x64.  The regression test is excluded on Windows.

Thanks, Harold

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Commit messages:
 - 8285792: Posix signal handler modification checking issues.

Changes: https://git.openjdk.org/jdk/pull/9631/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9631&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8285792
  Stats: 194 lines in 5 files changed: 172 ins; 4 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/9631.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9631/head:pull/9631

PR: https://git.openjdk.org/jdk/pull/9631