use C11 atomics and remove c++ code from utils_concurrency.h

remove C++ code related to atomics from utils_concurrency.h and use C11 atomics instead

```
#else /* __cplusplus */
#include <atomic>
#define _Atomic(X) std::atomic<X>

// TODO remove cpp code from this file
using std::memory_order_acq_rel;
using std::memory_order_acquire;
using std::memory_order_relaxed;
using std::memory_order_release;

#endif /* __cplusplus */
```
