[OpenMP] Only put retain for NVPTX so it can be optimized out for AMD

Summary:
This is a hack that only NVPTX needs.

Author: jhuber6

offload/DeviceRTL/src/Misc.cpp

@@ -115,8 +115,12 @@ void *indirectCallLookup(void *HstPtr) {
 /// The openmp client instance used to communicate with the server.
 /// FIXME: This is marked as 'retain' so that it is not removed via
 /// `-mlink-builtin-bitcode`
+#ifdef __NVPTX__
 [[gnu::visibility("protected"), gnu::weak,
   gnu::retain]] rpc::Client Client asm("__llvm_rpc_client");
+#else
+[[gnu::visibility("protected"), gnu::weak]] rpc::Client Client asm("__llvm_rpc_client");
+#endif
 
 } // namespace impl
 } // namespace ompx