fix: disable some abi conflict tests on FreeBSD

On FreeBSD, symbol resolution when dlopening a shared object will always
favor symbols local to this shared object and thus our canary function will
never be called which breaks our abi conflict detection when abi1 is loaded
first.

Disable the test cases with this scenario on FreeBSD as we have no way
to fix this at the moment.

Change-Id: Ic0451ce61e21f94ece55429b41bf76db3ad74b3a
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>