[flang] [clang] [flang] Enable alias tags pass by default (PR #73111)

[Tom Eccles via cfe-commits]

tblah wrote:

> If you are in a rush to land this then this LGTM, but I would like the relationship between `-O{1|2|3|4}` and `-f{no}-alias-analysis` to be refined in a follow-up patch. Unless there's a good reason to avoid that? WDYT?

Thanks @banach-space, I will land this now and follow up later today.

The behavior you're commenting on was deliberate because to me, it feels wrong to enable alias analysis if there is an `-fno-alias-analysis` flag anywhere (and no `-falias-analysis`) as it it may not be obvious that -O implies `-falias-analysis`, and what `-O` does isn't documented anywhere.

But I don't feel strongly about it so I will follow up with a new patch later if you still feel that is worthwhile.

https://github.com/llvm/llvm-project/pull/73111