[flang] Document preprocessing of Fortran comments in macro actual args

Original-commit: flang-compiler/f18@f491b73636fe95ede63d9f402d14e6f29250f95b
Reviewed-on: https://github.com/flang-compiler/f18/pull/557
Tree-same-pre-rewrite: false
2 files changed
tree: 03ff3216f3e08f0eeca112bb7dfb12f46ae349bf
  1. flang/