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

[bratpiorka]

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 */

[KFilipek]

Compatible compilers support it after setting the proper C standard: set(CMAKE_C_STANDARD 11).
Atomics in C11 are experimentally supported since VS2022 @ devblog on this
and require experimental flag: /experimental:c11atomics.