[flang] Flang requiring openmp for a cuda compilation

I a mtrying to compile fortran cuda code, after building the flang-rt for cuda offloading, and when i run this command:
```
flang --offload-targets=nvptx64-nvidia-cuda -static-libflangrt -v --offload-arch=sm_89 --offloadlib \
test_cuda_fortran.cuf -L"$CUDA_LIB64" \
-lcudart_static -lcudadevrt -ldl -lrt -lpthread -lm \
-o test_cuda_fortran
```
I get the error:
```log
flang-21: error: '-fopenmp-targets' must be used in conjunction with a '-fopenmp' option compatible with offloading; e.g., '-fopenmp=libomp' or '-fopenmp=libiomp5'
```
now, am i doing something wrong, or is it a bug in flang? I don't use any openmp code in the file I'm trying to compile, so I don't see why should openmp be involved or needed.
version used is 21.1.2.