See https://evergreen.mongodb.com/task/cxx_driver_ubuntu1404_release_compile_and_test_with_shared_libs_6ffd4100c52c564efb90a99a92f870ca5bf23127_17_11_04_15_48_21
Came in as part of https://github.com/mongodb/mongo-cxx-driver/commit/9409656d88e9301edadd2ac70812db3900ba42f0
GitHub PR