* Document deviation from Linux man page, which is identical to musl.
  Man page wants always enabled user-provided abort handlers.
  Worst case logic bug, which this can introduce:
    + user disables SIGABRT handler to prevent tear down to last safe
      state
    + abort() gets called and enables user-provided SIGABRT handler
    + SIGABRT tears down to supposed last safe state instead of crash
    + Application, instead of crashing, continues
* Pid 1 within containers needs special handling.
  - fatal signals are not transmitted without privileges,
    so use exit as fallback
* Fix some signaling bits
* Add checks in Debug and ReleaseSafe for wrong sigprocmask