[clang] [CodeGen] [VTable] don't think linkonce vtable as unique (PR #197855)

[Richard Smith via cfe-commits]

zygoloid wrote:

> So an optimization pass that replaces `%pred` with `true` is sound under my proposed rule. Am I missing anything?

It's currently correct to replace
```llvm
load %p
```
with
```llvm
icmp eq %p, <something>
...
load %p
```
and profile-driven optimizations may wish to do exactly that. Your rule makes that transformation incorrect.

https://github.com/llvm/llvm-project/pull/197855