[flang-commits] [clang] [flang] [Flang] [Options] To be compatible with classic flang, add the -Mextend compilation option (PR #173833)

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TZT123-a11y wrote:

 @tblah Thank you for both suggestions!

1. **Options.td reorganization**: I've moved the classic flang options (`Mextend`) to the Flang-only options section as suggested. By placing them in the correct section, I've removed the explicit `Visibility` specifications.

2. **Conflict handling improvement**: I've updated the option conflict handling in `Flang.cpp` to use `Args.getLastArg()` for proper precedence. Now when users specify both options (e.g., `-Mextend` and `-ffixed-line-length=N`, or similar for the other classic options), the last one on the command line takes precedence, following the usual convention.

Both changes make the implementation cleaner and more consistent with LLVM's conventions.

https://github.com/llvm/llvm-project/pull/173833