Fix SuiteSparse3 UFConfig.h detection.

Change-Id: Ia59aefdb0ad7f713f76ed79692f2db4fa2821e5b
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 6f35e96..6be2873 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -222,7 +222,11 @@
   CERES_TEST(schur_eliminator)
   CERES_TEST(schur_ordering)
   CERES_TEST(solver_impl)
-  CERES_TEST(suitesparse)
+
+  IF (${SUITESPARSE_FOUND})
+    CERES_TEST(suitesparse)
+  ENDIF (${SUITESPARSE_FOUND})
+
   CERES_TEST(symmetric_linear_solver)
   CERES_TEST(triplet_sparse_matrix)
   CERES_TEST(trust_region_minimizer)