[libcpu]优化rv构建脚本中选择vendor目录的判断条件

libcpu/risc-v/SConscript

@@ -17,7 +17,7 @@ else :
     group += SConscript(os.path.join('common', 'SConscript'))
 
 # cpu porting code files
-if  rtconfig.CPU == "c906":
+if 'VENDOR' in vars(rtconfig) and rtconfig.VENDOR != '':
     group = group + SConscript(os.path.join(rtconfig.VENDOR, rtconfig.CPU, 'SConscript'))
 elif rtconfig.CPU in list:
     group = group + SConscript(os.path.join(rtconfig.CPU, 'SConscript'))