fix linux tests, link statically

CMakeLists.txt

CMakeModules/testing_cpp.cmake

common/cpp/include/system_wrappers/io.h

common/cpp/include/system_wrappers/system_io.h

common/cpp/src/system_io.cpp

common/cpp/src/system_io_linux.cpp

common/cpp/src/system_io_windows.cpp

examples/worker/process_folder/CMakeLists.txt

tests/system_io/read_files_in_folder/cleanup_linux.sh

tests/system_io/read_files_in_folder/setup_linux.sh

tests/worker/connect_multithread/CMakeLists.txt

tests/worker/connect_multithread/content_multithread.cpp

tests/worker/next_multithread/CMakeLists.txt

worker/api/cpp/unittests/test_folder_broker.cpp