[clang] [clang] Allow devirtualisation of indirect calls to final virtual methods (PR #165341)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> And also, when bootstrapping, have you met errors like: `undefined symbol: clang::ImplicitConceptSpecializationDecl::~ImplicitConceptSpecializationDecl()`? There are other similar cases.
> 
> The common point of these decl is, they have a virtual destructor but they don't have any other virtual function. This is why my previous patch wrote: [ChuanqiXu9 at 40ceabe#diff-9f23818ed51d0b117b5692129d0801721283d0f128a01cbc562353da0266d7adR1375-R1382](https://github.com/ChuanqiXu9/llvm-project/commit/40ceabea69d20e4c8b0e5415e4f6c0b37c6b863a#diff-9f23818ed51d0b117b5692129d0801721283d0f128a01cbc562353da0266d7adR1375-R1382)

I haven't but I may try an assertion-free build because I see assertions in the baseline

https://github.com/llvm/llvm-project/pull/165341