Fixed VC compilation error on the JacobiSVD module.

Eigen/src/SVD/JacobiSVD.h

diff --git a/Eigen/src/SVD/JacobiSVD.h b/Eigen/src/SVD/JacobiSVD.h
index 4b69e67..d6b4561 100644
--- a/Eigen/src/SVD/JacobiSVD.h
+++ b/Eigen/src/SVD/JacobiSVD.h
@@ -26,20 +26,21 @@
 #define EIGEN_JACOBISVD_H
 
 // forward declarations (needed by ICC)
+// the empty bodies are required by VC
 template<typename MatrixType, unsigned int Options, bool IsComplex = NumTraits<typename MatrixType::Scalar>::IsComplex>
-struct ei_svd_precondition_2x2_block_to_be_real;
+struct ei_svd_precondition_2x2_block_to_be_real {};
 
 template<typename MatrixType, unsigned int Options,
          bool PossiblyMoreRowsThanCols = (Options & AtLeastAsManyColsAsRows) == 0
                                          && (MatrixType::RowsAtCompileTime==Dynamic
                                              || (MatrixType::RowsAtCompileTime>MatrixType::ColsAtCompileTime))>
-struct ei_svd_precondition_if_more_rows_than_cols;
+struct ei_svd_precondition_if_more_rows_than_cols {};
 
 template<typename MatrixType, unsigned int Options,
          bool PossiblyMoreColsThanRows = (Options & AtLeastAsManyRowsAsCols) == 0
                                          && (MatrixType::ColsAtCompileTime==Dynamic
                                              || (MatrixType::ColsAtCompileTime>MatrixType::RowsAtCompileTime))>
-struct ei_svd_precondition_if_more_cols_than_rows;
+struct ei_svd_precondition_if_more_cols_than_rows {};
 
 /** \ingroup SVD_Module
   * \nonstableyet