Use bridge script for SConscript

bsp/stm32/stm32l476-st-nucleo/SConscript

-# for module compiling
+# RT-Thread scons bridge
 import os
-Import('RTT_ROOT')
+from building import *
 
-cwd = str(Dir('#'))
+cwd = GetCurrentDir()
 objs = []
 list = os.listdir(cwd)