[PATCH] Move the signal handling logic into sanitizer_common

[Dmitry Vyukov]

  I do not understand why we have handle_segv/allow_user_segv_handler separately?
  0/1 combination is senseless, while 1/0 is questionable (users that do not set own handler do not care, and users who set own handler do it for some reason and do not want it to be silently ignored under tools)
  I think we need a single handle_segv flag, and allow to always override our handler?
  When do we want to not set our handler? Probably we can do it w/o flags at all.

http://llvm-reviews.chandlerc.com/D2605