src: backport fix for SIGINT crash on FreeBSD

This is a backport of b64983d7.

Original commit message:

  src: reset signal handler to SIG_DFL on FreeBSD

  FreeBSD has a nasty bug with SA_RESETHAND reseting the SA_SIGINFO,
  that is in turn set for a libthr wrapper. This leads to a crash.
  Work around the issue by manually setting SIG_DFL in the signal
  handler.

  Fix: https://github.com/joyent/node/issues/9326
  PR-URL: https://github.com/iojs/io.js/pull/1218


Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Fixes #9326.

Reviewed-By: Trevor Norris <trev.norris@gmail.com>
PR-URL: https://github.com/joyent/node/pull/14184