shared_mutex type name not found

I'm able to include shared_mutex header in my project by:

#include <shared_mutex>

and I'm able to see the shared mutex definitions.

but when I trying to init a shared lock by:

std::shared_mutex mutex_;
std::shared_lock lock_;
std::shared_timed_mutex m_;

xcode complains the type names not found.

Xcode:Version 7.3.1 (7D1014)

OSX: 11.11.6

LLVM 7.1

Any ideas?