add depend PKG_USING_WEBCLIENT

SConscript

@@ -4,6 +4,6 @@ cwd     = GetCurrentDir()
 src     = Glob('*.c')
 CPPPATH = [cwd]
 
-group = DefineGroup('WebClient', src, depend = ['RT_USING_LWIP'], CPPPATH = CPPPATH)
+group = DefineGroup('WebClient', src, depend = ['RT_USING_LWIP'，'PKG_USING_WEBCLIENT'], CPPPATH = CPPPATH)
 
 Return('group')