[llvm] Update cloning of the DirectXShaderCompiler repo to not include DXC tests (PR #122178)

[Brian Favela via llvm-commits]

bfavela wrote:

> This seems reasonable enough.
> 
> It does look like @llvm-beanz explicitly included the `-DLLVM_INCLUDE_TESTS` flag when he first implemented this, so it would be best to get an explicit sign off from him.

The flag should be "off". The intention here is to remove the test infrastructure completely from being built so as to not rely on external programs existing like TAEF.

https://github.com/llvm/llvm-project/pull/122178