package/babeltrace2: fix tests with uclibc

It should be noted that upstream does not want to add a --disable-tests
option: https://review.lttng.org/c/babeltrace/+/4075

Fixes:
 - http://autobuild.buildroot.org/results/1e50e1ff90c1ac2af2223365dc0cd6e1914bcd75



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>