Correction to cmake rules for libmv/ceres

libmv still requires optimization switched off because
of some incompatibility of SSBA and MSVC optimizer which
makes bundle adjustment work just wrong.

This shall not be an issue for Ceres and no need to
disable optimization for extern_ceres

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54623 954f8c5b-7b00-dc11-b283-0030488c597c