Add default Eigen install location on Windows to search paths.
Add default Eigen install location on Windows to search paths.

Change-Id: If2e9999b04550269c94a86b8512d9dcc2842b91d

DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,DougFirErickson/ceres-solver,DougFirErickson/ceres-solver,ysonggit/ceres-solver,whuaegeanse/ceres-solver,ysonggit/ceres-solver,ysonggit/ceres-solver,ysonggit/ceres-solver,whuaegeanse/ceres-solver,DougFirErickson/ceres-solver