JULIA_CUDA_USE_BINARY_BUILDER=false
needs to be set for each process. One way could be to put it in ~.bashrc or similar, another way to set it explicitly everywhere, i.e. the idea is:
mpiexec -n 2 'JULIA_CUDA_USE_BINARY_BUILDER=false julia alltoall_test.jl'
Maybe you will need to put JULIA_CUDA_USE_BINARY_BUILDER=false julia alltoall_test.jl
in a shell script and call
mpiexec -n 2 my_julia_multi_gpu_app.sh