[flang] [clang] [flang] Update -falias-analysis help text (PR #73548)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space approved this pull request.

Thanks, LGTM!

> @banach-space I'm happy to change the behavior too if you'd prefer that

That would be great, but could be done independently. Up to you!

In general, I feel that `-f{no-}alias-analysis` interacts with `-O{#N}` in a way that should be avoided. But I'd need to look more into how `-O{#N}` are defined to have a more informed opinion. So just restricting this option for now (provided it still work for you in the intended way) should be fine.

https://github.com/llvm/llvm-project/pull/73548