`LegalizeDataValuesInRegion` is intended to replace the SSA values used
in a region with the output of data operations, but misses the handling
of the OpenACC `host_data` construct. As a result, currently
```
!$acc host_data use_device(%var)
...%var...
!$acc end host_data
```
is lowered to
```
%dev_var = acc.use_device(%var)
acc.host_data data_operands(%dev_var) {
...%var...
}
```
This pull request updates the LegalizeDataValuesInRegion to handle
HostDataOp such that lowering results in
```
%dev_var = acc.use_device(%var)
acc.host_data data_operands(%dev_var) {
...%dev_var...
}
```
3633de7029