[flang] Changes per the review comments. The majority of the changes are simply

[flang] Changes per the review comments. The majority of the changes are simply
to rename identifiers to meet the project (not LLVM) coding standard.
Includes a home brew of FileCheck for testing.

Original-commit: flang-compiler/f18@bb15490cc02327773cb680597226346f02cd4dd0
Reviewed-on: https://github.com/flang-compiler/f18/pull/170
Tree-same-pre-rewrite: false