The 'set' lowering is pretty trivial. 'device_type' is a little more
restricted since both the MLIR-Dialect and language limit it to only 1
value (as confirmed by standards-discussion).
This patch implements 'set', with 'device_type', since 'set' requires at
least 1 clause, and this is the least difficult to implement at the
moment.
77db154cf9