[clang] [llvm] [ValueTracking] Return true for AddrSpaceCast in canCreateUndefOrPoison (PR #144686)

[Wenju He via llvm-commits]

wenju-he wrote:

> For the purposes of this PR, I think you should only change canCreateUndefOrPoison to return true and just eat the regressions. We can follow up with using isValidAddrSpaceCast() in a followup, because it will be less straightforward. I'm not willing to accept direct use of TTI in ValueTracking without laundering it through an abstraction first (see https://discourse.llvm.org/t/constant-propagation-for-target-specific-intrinsics/85881/5).

thanks @nikic 
Shall I file an issue for the task of using isValidAddrSpaceCast()?

https://github.com/llvm/llvm-project/pull/144686