[flang] Refactor some lib/evaluate headers for sanity

Original-commit: flang-compiler/f18@9530378c39d0206a93eafd7d19b7f52c82e8f904
Reviewed-on: https://github.com/flang-compiler/f18/pull/219
Tree-same-pre-rewrite: false
8 files changed
tree: f071c22b1e114a7354d1b0871eed021662903727
  1. flang/