add extern C when C++

Author: m-fila

compile/include/JetReconstruction.h

@@ -15,6 +15,10 @@
 #ifndef JET_RECONSTRUCTION_JL_H_
 #define JET_RECONSTRUCTION_JL_H_
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <stddef.h>
 
 /*Special states in a history.*/
@@ -341,4 +345,8 @@ jetreconstruction_StatusCode jetreconstruction_inclusive_jets(
     const jetreconstruction_ClusterSequence *clustersequence, double ptmin,
     jetreconstruction_JetsResult *result);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* JET_RECONSTRUCTION_JL_H_ */