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

[Juan Manuel Martinez Caamaño via llvm-commits]

https://github.com/jmmartinez approved this pull request.

Thanks! I didn't know about this (in another job, we used to `%{tool}`).

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