Implement c++03 compatible fix for changeset 7a43af1a33

unsupported/Eigen/src/FFT/ei_fftw_impl.h

@@ -231,6 +231,8 @@ namespace internal {
   protected:
       typedef fftw_plan<Scalar> PlanData;
 
+      typedef Eigen::numext::int64_t int64_t;
+
       typedef std::map<int64_t,PlanData> PlanMap;
 
       PlanMap m_plans;

unsupported/test/FFTW.cpp

@@ -8,7 +8,6 @@
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #include "main.h"
-#include <cstdint>
 #include <unsupported/Eigen/FFT>
 
 template <typename T>