Add the necessary defines for HAVE_PIPE2 for NetBSD and OpenBSD depending
on OS version when pipe2(2) was added. This also fixes the compile error
on NetBSD if -Werror=unused-function for ignore_sigpipe() as the
HAVE_PIPE2 tree is prior to O_NOSIGPIPE in create_pipe().

Change-Id: Ic8f875e34ef826a7bf046c77588afecaa097deca
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>