[llvm] [SPIR-V] Add SPIRV-Tools for testing (PR #73044)

[Natalie Chouinard via llvm-commits]

sudonatalie wrote:

I see the bot failure, but I'm not yet sure why `@LLVM_INCLUDE_SPIRV_TOOLS_TESTS@` is being substituted with `OFF` while other cmake vars in the file are being substituted with `0`. Looking into it.

https://github.com/llvm/llvm-project/pull/73044