[llvm] [SelectionDAG] Use unaligned store to legalize `EXTRACT_VECTOR_ELT` type when Stack is non-realignable (PR #98176)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> "This leads to the generation of a vmovdqa instruction, which can lead to a General Protection Fault. Here is the link to the godbolt demo: https://godbolt.org/z/33h7YGc5K"
> 
> Given this, should this backported to 19.x or is that not a problem there?

I think it's good to backport.

https://github.com/llvm/llvm-project/pull/98176