Fix DLL builds and c++ lapack declarations.

Fix DLL builds and c++ lapack declarations.

We need separate EIGEN_BUILD_* macros for BLAS/LAPACK for dllexport/dllimport since when building the lapack library, we need to export lapack symbols but import blas symbols. We also need ".def" files for windows to allow the fortran symbols to be exported in the dll.

There were several LAPACK functions missing from lapack.h that are implemented in Eigen. Added those functions to the lapack.h header, and corrected the complex-type scalar inputs for consistency.

Fixes #2980 (closed).