fixed visual c++ 6.0 build

src/iocsh/iocsh.cpp

@@ -597,6 +597,8 @@ static void varHandler(const iocshVarDef *v, const char *setString)
     }
 }
 
+extern "C" {
+
 static void varCallFunc(const iocshArgBuf *args)
 {
     struct iocshVariable *v;
@@ -615,6 +617,8 @@ static void varCallFunc(const iocshArgBuf *args)
     }
 }
 
+}
+
 /*
  * Dummy internal commands -- register and install in command table
  * so they show up in the help display