[flang] Tweaks to provenance data structures, in preparation for better module file support.

Original-commit: flang-compiler/f18@a7b7b2b6801aa8beadde3d05a29d40057a5f264e
Reviewed-on: https://github.com/flang-compiler/f18/pull/151
Tree-same-pre-rewrite: false
14 files changed
tree: 3f3b9080d50979dac6ec3226fbbcf4f1ae47bb01
  1. flang/