This fixes the following error on my Ubuntu 18.04 with CMake 3.10.2:
CMake Error at cmake/TestCase.cmake:8 (target_link_libraries):
Target "catch_main" of type OBJECT_LIBRARY may not be linked into another
target. One may link only to STATIC or SHARED libraries, or to executables
with the ENABLE_EXPORTS property set.
Call Stack (most recent call first):
test/unit/CMakeLists.txt:6 (test_case)
a5f80d0608