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
1 file changed