[llvm] [SPIR-V] Use ToolSubst for spirv-tools lit substitutions (PR #192462)

[Nick Sarnie via llvm-commits]

sarnex wrote:

also we probably need a similar fix here if you have time

https://github.com/llvm/llvm-project/blob/e5bb8046685769be4f1ed685a583a8a615f8abc8/clang/test/Tooling/lit.local.cfg#L2

https://github.com/llvm/llvm-project/pull/192462