cmake HAVE_UNW_STEP examples

google/glog CMakeLists.txt :102 

check_cxx_symbol_exists (unw_step libunwind.h HAVE_UNW_STEP)

google/glog CMakeLists.txt :110 

endif (HAVE_UNW_GET_REG AND HAVE_UNW_GETCONTEXT AND HAVE_UNW_INIT_LOCAL AND HAVE_UNW_STEP)