[flang] Add missing dependency on tablegen files

This issue was raised on https://github.com/llvm/llvm-project/issues/64268.

`flang/lib/Optimizer/Transforms/SimplifyIntrinsics.cpp` includes
`flang/Optimizer/HLFIR/HLFIRDialect.h` and might fails if the HLFIR related
tablegen files have not been generated.

Reviewed By: vzakhari

Differential Revision: https://reviews.llvm.org/D156751