The flag unsafe-loop-optimizations is currently set when GCC version is 4.7, 5.x or 6.x. This triggers a warning when trying to compile c++ files that use range based for loop:
../../../test/cppsuite/test_harness/thread_manager.cxx: In destructor 'test_harness::thread_manager::~thread_manager()': ../../../test/cppsuite/test_harness/thread_manager.cxx:35:21: error: missed loop optimization, the loop counter may overflow [-Werror=unsafe-loop-optimizations] for (auto &it : _workers) {
This flag should be disabled when compiling c++ files.