Add TBB information to Ceres version string.

Change-Id: I8ec87ee57bcdcf54f105b4c368432d93ada2ea59

internal/ceres/solver_utils.cc

diff --git a/internal/ceres/solver_utils.cc b/internal/ceres/solver_utils.cc
index 7f4ff7e..084caeb 100644
--- a/internal/ceres/solver_utils.cc
+++ b/internal/ceres/solver_utils.cc
@@ -30,7 +30,12 @@
 
 #include <string>
 
+#include "ceres/internal/config.h"
+
 #include "Eigen/Core"
+#ifdef CERES_USE_TBB
+#include "tbb/tbb_stddef.h"
+#endif  // CERES_USE_TBB
 #include "ceres/internal/port.h"
 #include "ceres/solver_utils.h"
 #include "ceres/version.h"
@@ -43,6 +48,10 @@
   CERES_TO_STRING(EIGEN_MAJOR_VERSION) "."                           \
   CERES_TO_STRING(EIGEN_MINOR_VERSION)
 
+#define CERES_TBB_VERSION                          \
+  CERES_TO_STRING(TBB_VERSION_MAJOR) "."           \
+  CERES_TO_STRING(TBB_VERSION_MINOR)
+
 std::string VersionString() {
   std::string value = std::string(CERES_VERSION_STRING);
   value += "-eigen-(" + std::string(CERES_EIGEN_VERSION) + ")";
@@ -75,6 +84,12 @@
   value += "-no_openmp";
 #endif
 
+#ifdef CERES_USE_TBB
+  value += "-tbb-(" + std::string(CERES_TBB_VERSION) + ")";
+#else
+  value += "-no_tbb";
+#endif
+
 #ifdef CERES_NO_CUSTOM_BLAS
   value += "-no_custom_blas";
 #endif