Resolves: https://github.com/llvm/llvm-project/issues/164150
C++26 allows for constexpr packs in structured bindings. This is a new
feature (the code doesn't compile on lower the -std=c++26) and so was
previously unhandled in clang.
This makes clang aware of packs and handle them as one constant unit
instead of materializing them as separate mutable reference temporaries
allowing llvm to optimize them.
This turns the example code from the issue into this as you would expect
without compiling for zen 5 (the good codegen described).
```asm
movq %rdi, %rax
movups (%rsi), %xmm0
movups %xmm0, (%rdi)
movups (%rdx), %xmm0
movups %xmm0, 16(%rdi)
retq
```
