Add a semantic check to detect when the same variable appears multiple
times in `use_device` clauses on the same `host_data` directive. While
the OpenACC specification does not explicitly prohibit this, allowing
duplicates is likely a user error and provides no additional semantics.
A similar restriction was already in place for `private`,
`firstprivate`, and `reduction` clauses on compute constructs. This
change extends that behavior to `use_device` on `host_data`.
Error message:
`'<var>' appears in more than one USE_DEVICE clause on the same
HOST_DATA directive`
c91ab61de7