Fix compilation error on systems without SuiteSparse installed
Fix compilation error on systems without SuiteSparse installed

Issue was caused by declaring class PerThreadContext with some
members of choldmod-specific types. This class in only used from
an #ifndef CERES_NO_SUITESPARSE block and solved compilation error
by simply wrapping PerThreadContext with the same #ifndef block.

Change-Id: Icdc329073fcbd4a328e41ea8c0af0962e9c34ba8

jmwalls/ceres-solver-fork,entylop/ceres-solver,DougFirErickson/ceres-solver,timfel/ceres-bin,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,timfel/ceres-bin,entylop/ceres-solver,ikoruk/ceres-solver,entylop/ceres-solver,ysonggit/ceres-solver,whuaegeanse/ceres-solver,kartikkumar/ceres-solver,stonier/ceres_solver,ikoruk/ceres-solver,ikoruk/ceres-solver,stonier/ceres_solver,timfel/ceres-bin,ikoruk/ceres-solver,timfel/ceres-bin,stonier/ceres_solver,jmwalls/ceres-solver-fork,kartikkumar/ceres-solver,ikoruk/ceres-solver,entylop/ceres-solver,kartikkumar/ceres-solver,DougFirErickson/ceres-solver,kartikkumar/ceres-solver,jmwalls/ceres-solver-fork,stonier/ceres_solver,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,jmwalls/ceres-solver-fork,ysonggit/ceres-solver,ysonggit/ceres-solver,DougFirErickson/ceres-solver,ysonggit/ceres-solver