suitesparse_test is enabled even when -DSUITESPARSE=OFF.

Fixed so that suitesparse_test is not compiled if SuiteSparse
support is not enabled.

Change-Id: If6430c3eb42548742d667d876492fff5687fd87d

internal/ceres/CMakeLists.txt

diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index d59469c..a981d59 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -198,7 +198,9 @@
   ENDIF (GFLAGS)
   CERES_TEST(schur_ordering)
   CERES_TEST(solver_impl)
-  CERES_TEST(suitesparse)
+  IF (SUITESPARSE)
+    CERES_TEST(suitesparse)
+  ENDIF(SUITESPARSE)
   CERES_TEST(symmetric_linear_solver)
   CERES_TEST(triplet_sparse_matrix)
   CERES_TEST(trust_region_minimizer)