Implement omp_get_mapped_ptr until it is available

omp_get_mapped_ptr is only for omp >= 5.1
gcc and clang still does not implement it

Author: alkino

coreneuron/gpu/nrn_acc_manager.cpp

@@ -48,7 +48,15 @@ T* cnrn_target_deviceptr(const T* h_ptr) {
 #if defined(CORENEURON_ENABLE_GPU) && !defined(CORENEURON_PREFER_OPENMP_OFFLOAD) && defined(_OPENACC)
     return acc_deviceptr(const_cast<T*>(h_ptr));
 #elif defined(CORENEURON_ENABLE_GPU) && defined(CORENEURON_PREFER_OPENMP_OFFLOAD) && defined(_OPENMP)
-    return static_cast<T*>(omp_get_mapped_ptr(const_cast<T*>(h_ptr), omp_get_default_device()));
+    T* _h_ptr = const_cast<T*>(h_ptr);
+    T *d_ptr = nullptr;
+
+    nrn_pragma_omp(target data use_device_ptr(_h_ptr))
+    {
+        d_ptr = _h_ptr;
+    }
+
+    return d_ptr;
 #else
     throw std::runtime_error("cnrn_target_deviceptr() not implemented without OpenACC/OpenMP and gpu build");
 #endif