bsp/include/jffs2_flashdev: Added CPP guards

Closes #5280

bsps/include/dev/flash/jffs2_flashdev.h

@@ -32,6 +32,10 @@
 #include <rtems/jffs2.h>
 #include <rtems/rtems/status.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 /**
  * This function mounts a JFFS2 partition over the specified region on a
  * flashdev-controlled device file.
@@ -53,4 +57,8 @@ rtems_status_code jffs2_flashdev_mount(
   bool read_only
 );
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif /* JFFS2_FLASHDEV_H */