创建，添加sdram

rt-thread/components/net/lwip-dhcpd/SConscript

@@ -0,0 +1,13 @@
+from building import *
+
+cwd = GetCurrentDir()
+CPPPATH = [cwd]
+
+if GetDepend('RT_USING_LWIP141'):
+    src = ['dhcp_server.c']
+else:
+    src = ['dhcp_server_raw.c']
+
+group = DefineGroup('lwIP', src, depend = ['RT_USING_LWIP', 'LWIP_USING_DHCPD'], CPPPATH = CPPPATH)
+
+Return('group')