Fix: Handle SIGBUS in sessiond and consumerd

Fix: Handle SIGBUS in sessiond and consumerd

There is an issue with the security model of lib ring buffer (lttng-ust)
vs SIGBUS handling by consumer daemon. We do not handle SIGBUS in the
consumer daemon. An application using ftruncate on a ring buffer shm
could cause the consumer to be killed with SIGBUS.

Wire up SIGBUS handling in the session daemon as well given that it also
uses liblttng-ust-ctl.

This depends on "liblttng-ust-ctl: Implement SIGBUS handling" in
lttng-ust, which extends the API of liblttng-ust-ctl, which requires
the user application to define the TLS sigbus state with
DEFINE_LTTNG_UST_SIGBUS_STATE(). It therefore needs to be introduced in
locked-step between lttng-ust and lttng-tools.

Considering that this change in liblttng-ust-ctl modifies the ABI, it is
done with a major soname version bump of the library, so it is allowed
to break the API.

Depends-on: lttng-ust: I7ade988e3e68a87930fbcee3e14e59c3fb66e755

Fixes: #1284
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I76a91616bd35b21c5e891c8306c73ed5e8725ebb