Automerge: [flang][cuda] Use default stream when calling cudaStreamSynchronize without arg (#182623)

Author: clementval

flang-rt/lib/cuda/stream.cpp

@@ -35,8 +35,7 @@ int RTDECL(CUFStreamSynchronize)(cudaStream_t stream) {
 }
 
 int RTDECL(CUFStreamSynchronizeNull)() {
-  cudaStream_t defaultStream = 0;
-  return cudaStreamSynchronize(defaultStream);
+  return cudaStreamSynchronize(RTNAME(CUFGetDefaultStream)());
 }
 }