C++11 'yield' is not a member of 'std::this_thread'
原因：GCC没有定义这个宏：_GLIBCXX_USE_SCHED_YIELD
解决办法：编译时加上选项：-D_GLIBCXX_USE_SCHED_YIELD
或者：长远打算修改gcc的c++config.h文件去定义这个宏。
详情：'yield' is not a member of 'std::this_thread'
see also： C++11 error: ‘sleep_for’ is not a member of ‘std::this_thread’
