Add additional cuda-toolkit location variable used by py-torch (#46245)

superceds #46128

Co-authored-by: Robert Underwood <runderwood@anl.gov>

var/spack/repos/builtin/packages/py-torch/package.py

@@ -526,6 +526,7 @@ def enable_or_disable(variant, keyword="USE", var=None):
 
         enable_or_disable("cuda")
         if "+cuda" in self.spec:
+            env.set("CUDA_TOOLKIT_ROOT_DIR", self.spec["cuda"].prefix)  # Linux/macOS
             env.set("CUDA_HOME", self.spec["cuda"].prefix)  # Linux/macOS
             env.set("CUDA_PATH", self.spec["cuda"].prefix)  # Windows
             self.torch_cuda_arch_list(env)