[llvm] [GlobalISel] Fix null deref when target has no stack guard variable (PR #224252)

[via llvm-commits]

tfzee wrote:

@arsenm if I have answered all your questions, you see no further issues and no further reviews are required could you merge it? Since I don't have access. :)
Thank you 

https://github.com/llvm/llvm-project/pull/224252