Add cuda_is_configured() build macro for testing whether CUDA was enabled at configure time.

Change: 141474932

third_party/gpus/cuda/build_defs.bzl.tpl

@@ -15,12 +15,16 @@ def if_cuda(if_true, if_false = []):
         "//conditions:default": if_false
     })
 
+def cuda_is_configured():
+    """Returns true if CUDA was enabled during the configure process."""
+    return %{cuda_is_configured}
+
 def if_cuda_is_configured(x):
     """Tests if the CUDA was enabled during the configure process.
 
     Unlike if_cuda(), this does not require that we are building with
     --config=cuda. Used to allow non-CUDA code to depend on CUDA libraries.
     """
-    if %{cuda_is_configured}:
+    if cuda_is_configured():
       return x
     return []