add serial.lsts to default.lsts

Author: alex-s168

PLATFORM/C/LIB/default.lsts

@@ -47,3 +47,4 @@ import PLATFORM/C/LIB/regex.lm;
 import PLATFORM/C/LIB/cmp.lsts;
 import PLATFORM/C/LIB/print.lsts;
 import PLATFORM/C/LIB/umbra.lsts;
+import PLATFORM/C/LIB/serial.lsts;