make compatible with C

src/lammpsplugin.h

@@ -15,8 +15,9 @@
 #define LMP_LAMMPSPLUGIN_H
 
 // C style API and data structure required for dynamic loading
-
+#ifdef __cplusplus
 extern "C" {
+#endif
 
 typedef void *(lammpsplugin_factory1) (void *);
 typedef void *(lammpsplugin_factory2) (void *, int, char **);
@@ -41,6 +42,9 @@ typedef void (*lammpsplugin_initfunc)(void *, void *, void *);
 // to load a plugin; uses C bindings
 
 void lammpsplugin_init(void *, void *, void *);
+
+#ifdef __cplusplus
 }
+#endif
 
 #endif