Simplify dylib driver switch.
Simplify dylib driver switch.

Co-authored-by: Geoffrey Martin-Noble <1b50226fb1523bae5dacd737e03523712e2ae5a7@google.com>
iree-org/iree,google/iree,google/iree,iree-org/iree,google/iree,google/iree,google/iree,iree-org/iree,iree-org/iree,google/iree,iree-org/iree,iree-org/iree,google/iree,iree-org/iree