Implement Memory Fence Functions in header

Enabled __llvm_fence_* functions for seq_cst.

src/device_util.cpp

@@ -155,6 +155,3 @@ __host__ __device__ int max(int arg1, int arg2) {
 }
 
 __host__ void* __get_dynamicgroupbaseptr() { return nullptr; }
-
-
-__device__ void __threadfence_system(void) { std::atomic_thread_fence(std::memory_order_seq_cst); }

src/device_util.h

@@ -125,7 +125,6 @@ __device__ double __hip_fast_dsqrt_rd(double x);
 __device__ double __hip_fast_dsqrt_rn(double x);
 __device__ double __hip_fast_dsqrt_ru(double x);
 __device__ double __hip_fast_dsqrt_rz(double x);
-__device__ void __threadfence_system(void);
 
 float __hip_host_j0f(float x);
 double __hip_host_j0(double x);