[llvm-branch-commits] [flang][runtime] Added custom visitor for IoStatementState variants. (PR #85179)

[Slava Zakharin via llvm-branch-commits]

https://github.com/vzakhari created https://github.com/llvm/llvm-project/pull/85179

The visitor only allows Internal.*IoStatementState variants to be visited.
In case another variant is met a runtime error is produced.
During the device compilation the other variants' classes are not referenced,
which, for example, helps to avoid warnings about __host__ only
methods referenced in __device__ code.

I had problems parameterizing the Fortran::common visitor to limit
the allowed variants, but I can give it another try if creating
a copy looks inappropriate.