Ensure build paths for dependencies are searched in FindPackage(Ceres)

- Append to hint locations used by FindPackage scripts for public
  dependencies (glog & Eigen) the locations of the dependencies when
  Ceres was built.
- This means that the user should not have to supply them again when
  using find_package(Ceres) even if they are installed in a
  non-standard location.

Change-Id: I9550de91025ba47f01f1ea3c3fefe80fe38d14ff