Block signals before invoking special or user handlers

1. Block signals marked in sa_mask before invoking user handler
   if not in old style.
2. Block all signals before invoking special signal handler.

Change-Id: Ie1283e97ed28ee3421df584352cd62cb107264bc
Signed-off-by: jgu21 <jinghui.gu@intel.com>
2 files changed