[libunwind] [PAC][libunwind] Pass ptrauth-qualified values as const references (PR #173765)

[Daniil Kovalev via cfe-commits]

kovdan01 wrote:

Thanks @ojhunt for your feedback on this!

> This looks good to me, if we encounter perf issues we might want to consider adding something like

Yeah, just please let me (and @asl) know if you encounter some. We do not measure performance for unwinding stuff, so we'll rely on your benchmarks :)

BTW, I suppose that template aliasing like this `template <class T> using HardenedPtr  = T;` in your suggestion would not be applicable for libunwind since we need to maintain some backward compatibility with old C++ standards while such template aliases are a C++11 feature. And it looks like that `typedef`'s are used instead of `using` directives in libunwind, and it's probably the reason why.

But I might be mistaken and probably we can use modern features in non-public headers. 

https://github.com/llvm/llvm-project/pull/173765