Disabled warning C4251 Added the files disable_warnings.h and reenable_warnings.h which need to be included by every file that uses the macro CERES_EXPORT.

Change-Id: I176326a600d094a4524bac873564fcbf8efd2456

include/ceres/solver.h

@@ -40,6 +40,7 @@
 #include "ceres/iteration_callback.h"
 #include "ceres/ordered_groups.h"
 #include "ceres/types.h"
+#include "ceres/internal/disable_warnings.h"
 
 namespace ceres {
 
@@ -957,4 +958,6 @@ CERES_EXPORT void Solve(const Solver::Options& options,
 
 }  // namespace ceres
 
+#include "ceres/internal/reenable_warnings.h"
+
 #endif  // CERES_PUBLIC_SOLVER_H_