openmp 4.5 and cuda streams

Dear All,

I'm using clang 9.0.0 to compile a code which offloads sections of a code on a GPU using the openmp target construct.
I also use the nowait clause to overlap the execution of certain kernels and/or host<->device memory transfers.
However, using the nvidia profiler I've noticed that when I compile the code with clang only one cuda stream is active,
and therefore the execution gets serialized. On the other hand, when compiling with XLC I see that kernels are executed
on different streams. I could not understand if this is the expected behavior (e.g. the nowait clause is currently not supported),
or if I'm missing something. I'm using a NVIDIA Tesla P100 GPU and compiling with the following options:

-target x86_64-pc-linux-gnu -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_60

best wishes