env 工具 scons 错误

F:\work t-thread\bsp\stm32f429-armfly>scons —target=mdk5 -s

scons: warning: No version of Visual Studio compiler found - C/C++ compilers most likely not set correctly
File “F:\work t-thread\bsp\stm32f429-armfly\SConstruct”, line 32, in

新手各种问题啊，scons命令提示Visual Studio compiler 错误，这是什么鬼啊？