[OpenMP] Add pre sm_70 load hack back in (#138589)

Summary:
Different ordering modes aren't supported for an atomic load, so we just
do an add of zero as the same thing. It's less efficient, but it works.

Fixes https://github.com/llvm/llvm-project/issues/138560

offload/DeviceRTL/include/Synchronization.h

@@ -59,7 +59,11 @@ V add(Ty *Address, V Val, atomic::OrderingTy Ordering,
 template <typename Ty, typename V = utils::remove_addrspace_t<Ty>>
 V load(Ty *Address, atomic::OrderingTy Ordering,
        MemScopeTy MemScope = MemScopeTy::device) {
+#ifdef __NVPTX__
+  return __scoped_atomic_fetch_add(Address, V(0), Ordering, MemScope);
+#else
   return __scoped_atomic_load_n(Address, Ordering, MemScope);
+#endif
 }
 
 template <typename Ty, typename V = utils::remove_addrspace_t<Ty>>