GitLab

Implement the legacy SysV signal handling functions sighold(),
sigignore(), sigpause(), sigrelse(), and sigset() in terms of the newer
POSIX signal APIs.  As of POSIX 2013 the SysV signal APIs are deprecated
but still required.

Change-Id: I4ca40e3d706605a7d1a30dc76c78b2b24586387d
Signed-off-by: Greg Hackmann <ghackmann@google.com>