[clang] [lld] [lld][ELF][clang][MTE] Add generic -z memtag-* options (PR #187055)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> > I almost did not notice this patch as I am not added a reviewer. The clang change makes sense but can you extract the lld/ELF to a separate patch?
> > 
> > * lld: Add -z memtag-{mode,heap,stack}
> > * clang: Switch -fsanitize=memtag to use -z memtag-* linker flags
> 
> Sorry, I don't think I can add reviewers directly, I think I can just tag people in comments.
> 
> Anyway, two separate commits was my original plan, but @fmayer requested them to be merged together in a single one. The reason is that the lld patch breaks backwards compatibility by removing some flags, so we would have a commit with the clang driver which is incompatible with lld. That would also probably break some of the clang tests for memtag. In addition, if we split in two commits and only one gets reverted, the incompatiblity would pop up again; reverting as a single unit is better. This reasoning makes sense to me, @MaskRay do you still want them separate?

They should be separate in principle. I see that you removed options from `lld/ELF/Options.td` - which is acceptable for fr this Android feature and Android bundles clang and lld. So I think it's fine for this specific case.

https://github.com/llvm/llvm-project/pull/187055