RFR: 8292695: SIGQUIT and jcmd attaching mechanism does not work with signal chaining library [v2]

[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

Man Cao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into JDK-8292695
 - Install SIGBREAK handler only once
 - Fix whitespace
 - 8292695: SIGQUIT and jcmd attaching mechanism does not work with signal chaining library

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9955/files
  - new: https://git.openjdk.org/jdk/pull/9955/files/d1c3f4b7..d226de41

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9955&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9955&range=00-01

  Stats: 79479 lines in 1204 files changed: 35070 ins; 35295 del; 9114 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