tests/lib/conds: test clock compatibility post conditions

tests/lib/conds: test clock compatibility post conditions

Add tests for the clock class compatibility post conditions in
`iterator.c`.  There is one test for each `BT_ASSERT_POST_DEV` in
`assert_post_dev_clock_classes_are_compatible_one`.

`addClockClsCompatTriggers()` adds a bunch of triggers that make a
message iterator return two messages with incompatible clock classes.
The message types that play a role in the clock compatibility checks are
"stream beginning" and "message iterator inactivity".
`addClockClsCompatTriggers()` adds all possible combinations of using
these two message types for the first and second message.  Since it's
not possible to send a message iterator inactivity message without a
clock class, some cases are skipped.

The change in `Makefile.am` is needed for the test to work in builds
with `--enable-built-in-plugins`, for the `RunIn` utility to be able to
find the `utils` plugin.  This was not needed before, because all the
existing triggers make the program stop before `RunIn` attempts to load
the `utils` plugin.

Change-Id: Ib6c22923e4e9f02de64a87efddaee3c23d3891ea
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/11811
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>