RFR: 8292695: SIGQUIT and jcmd attaching mechanism does not work with signal chaining library

[Man Cao]

Hi all,

Could anyone review this bug fix? See https://bugs.openjdk.org/browse/JDK-8292695 for details.

I changed the temporary handler for SIGQUIT to use a dummy function, and use `os::signal()` to set it up, just as `os::initialize_jdk_signal_support()` does.
It is possible that just moving the `set_signal_handler(BREAK_SIGNAL, false);` in `install_signal_handlers()` outside of the window bounded by `JVM_{begin|end}_signal_setting()` could also fix this bug. However, `set_signal_handler()` and `JVM_HANDLE_XXX_SIGNAL()` are currently used for signals that support chaining and periodically check, which do not apply to SIGQUIT. I think it is cleaner to use different functions for SIGQUIT.

I also added a test to check that sending SIGQUIT should produce a thread dump on stdout, with and without using libjsig.so.

-Man

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Commit messages:
 - Fix whitespace
 - 8292695: SIGQUIT and jcmd attaching mechanism does not work with signal chaining library

Changes: https://git.openjdk.org/jdk/pull/9955/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9955&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292695
  Stats: 126 lines in 2 files changed: 110 ins; 12 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/9955.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9955/head:pull/9955

PR: https://git.openjdk.org/jdk/pull/9955