[lldb] [llvm] Define -DLLVM_BUILD_TELEMETRY to be used in ifdef (PR #126746)

[Pavel Labath via llvm-commits]

labath wrote:

.. and fix the code so that it uses the new macro name ? (You'll need to include llvm-config.h before you can use the macro, and I'd recommend doing a build with telemetry disabled to check that everything works as it should)

https://github.com/llvm/llvm-project/pull/126746