fix a few issues with unit tests
1. fix unused argument warnings - running ninja tests fails on my system
due to too many warnings.
2. fix google benchmark build - sometimes, when building from scratch
the build will fail due to compiler warnings. I don't know why it
only happens sometimes but I've instead added a warning suppression
as this is not an issue in our code.
3. fix memory leak I've found here: !3827 (comment 224369)
4. fix running two testcases with ninja test or ctest -R. Due to them
being dependent on dlopen they would automatically fail if the user
environemnt was not modified manually outside cmake. I've modified
LD_LIBRARY_PATH for those test cases, meaning you no longer need to
run it with LD_LIBRARY_PATH=. or similar prefix.
Reviewed-By: Robert Schmidt <robert.schmidt@openairinterface.org>