SCons构建分层目录结构

Directory Structure:

目录结构：

WorkSpace/root_dir
|_ SConstruct
|_ multipy
  |_ include
    |_ mul.h
  |_ src
    |_ mul.cpp
    |_ SConscript
|_ sum
  |_ include
    |_ sum.h
  |_ src
    |_ sum.cpp
    |_ SConscript
|_ src_main
  |_ main.cpp
  |_ SConscript
WorkSpace/root_d