减少绝对路径依赖，避免中间产物残留

Author: rcitach

bsp/novosns/ns800/libraries/HAL_Drivers/SConscript

@@ -4,10 +4,11 @@ from building import *
 import os
 
 cwd = GetCurrentDir()
+group = []
 src = ['drv_common.c']
 path = [cwd]
 
-group = SConscript(os.path.join(cwd, 'drivers', 'SConscript'))
+group = SConscript(os.path.join('drivers', 'SConscript'))
 group = group + DefineGroup('HAL_Drivers', src, depend = [''], CPPPATH = path)
 
 Return('group')