RFR: 8253742: POSIX signal code cleanup [v4]

[Gerard Ziemski]

> hi all,
> 
> Please review this followup to [JDK-8252324 Signal related code should be shared among POSIX platforms](https://bugs.openjdk.java.net/browse/JDK-8252324), where several issues were identified for a cleanup. This change addresses them all:
> 
> #1 David's feedback - removed non POSIX SIGNIFICANT_SIGNAL_MASK code
> 
> #2 David's feedback - used unblock_program_error_signals() on all platforms (reverted for JDK-8252533)
> 
> #3 David's feedback - used single JVM_handle_posix_signal API for all POSIX platforms (reverted for JDK-8255711)
> 
> #4 Coleen's feedback - cleanup header files in src/hotspot/os/posix/signals_posix.hpp
> 
> #5 Coleen's feedback - hid SR_signum assignment in src/hotspot/os/posix/signals_posix.hpp to avoid having to include <signal.h>
> 
> #6 Coleen's feedback - factored out print_signal_handlers()
> 
> #7 Thomas' feedback - factored out common POSIX os::SuspendedThreadTask::internal_do_task()
> 
> #8 Thomas's feedback - factored out common POSIX signal initialization code
> 
> #9 YaSuenag's feedback - used JVM_handle_posix_signal for the common API
> 
> #10 YaSuenag's feedback - unified logging out of the scope for this fix
> 
> #11 YaSuenag's feedback - memset usage in PosixSignals::jdk_misc_signal_init() correct?

Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:

  David's feedback

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/636/files
  - new: https://git.openjdk.java.net/jdk/pull/636/files/1c2726de..4d8f4f7b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=636&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=636&range=02-03

  Stats: 39 lines in 6 files changed: 0 ins; 33 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/636.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/636/head:pull/636

PR: https://git.openjdk.java.net/jdk/pull/636