[llvm] [SPIR-V] Add store legalization for ptrcast (PR #135369)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

Build failure seems unrelated. We got 2 broken SPIR-V tests: smoothstep & SV_GroupIndex, those are caused by a recently added validation in Vulkan1.3 which disallow the Linkage capability.
Unrelated to this PR.


https://github.com/llvm/llvm-project/pull/135369