[clang] [flang] [flang] Add nsw flag to do-variable increment with a new option (PR #91579)

[Yusuke MINATO via cfe-commits]

yus3710-fj wrote:

Windows build failed with the following message.

> fatal error C1060: compiler is out of heap space

I'll try re-running CI with an empty commit because it might have been happend by accident.


https://github.com/llvm/llvm-project/pull/91579