More clearly disable the inclusion of src/Core/arch/CUDA/Complex.h without CUDA

Author: ggael

Eigen/Core

@@ -206,7 +206,9 @@ using std::ptrdiff_t;
 
 // Specialized functors to enable the processing of complex numbers
 // on CUDA devices
+#ifdef EIGEN_CUDACC
 #include "src/Core/arch/CUDA/Complex.h"
+#endif
 
 #include "src/Core/util/IndexedViewHelper.h"
 #include "src/Core/ArithmeticSequence.h"