rocThrust and atomic path

When using the atomic path, block IDs are assigned by atomically incrementing a counter in global device memory. This produces a predictable ordering of block IDs for kernels that require path correctness.

The default rocThrust setting uses the atomic path only with gfx942 or gfx950 architectures.

This behavior can be changed through the ROCPRIM_USE_ATOMIC_BLOCK_ID environment variable. Set ROCPRIM_USE_ATOMIC_BLOCK_ID to 0, to never use the atomic path. Set ROCPRIM_USE_ATOMIC_BLOCK_ID to 2 to always use the atomic path. Set ROCPRIM_USE_ATOMIC_BLOCK_ID to 1 to return to the default behavior where the atomic path is used automatically only on gfx942 or gfx950 architectures.

Because using the atomic path can come at a performance cost, ROCPRIM_USE_ATOMIC_BLOCK_ID should be set to 2 only if there is a noticeable performance degradation or a deadlock in the rocThrust and rocPRIM kernels regardless of the underlying architecture.

ROCPRIM_USE_ATOMIC_BLOCK_ID should be set to 0 only in the case where neither the gfx942 or gfx950 architectures are being used.