1) Build with default option
  To build with default option:
  # scons

  To see help information with default option(the output may be different with different options):
  # scons -Q -h

  To clean the project:
  # scons -c

2) Build with options
  To build with options:
  # scons OPTION1=xxx OPTION2=xxx OPTION3=....

  To see help information:
  # scons OPTION1=xxx OPTION2=xxx OPTION3=.... -Q -h

  To clean the project:
  # scons OPTION1=xxx OPTION2=xxx OPTION3=.... -c

3) Examples
  To build default
  # scons
  To see default help
  # scons -Q -h
  To clean
  # scons -c

  To build android armeabi-v7a
  # scon BUILD_TARGET=Android CPU_ARCH=armeabi-v7a
  To see help
  # scon BUILD_TARGET=Android CPU_ARCH=armeabi-v7a -Q -h
  To clean
  # scon BUILD_TARGET=Android CPU_ARCH=armeabi-v7a -c

Note:
  1. To build android binary, android NDK should be newer than r8e(recommend r10).
  2. You may be asked to set some options. Besides set it in command line, you
can also set it by create a environment variable. Command line has higher priority.
If both are set, the command line value will be used.