If the attribute name is passed, then it is the one used to process the option
--target[s] of waf build. The board name should be used only in configuration
time. The build targets should be board/platform agnostic.
Now, instead of using `waf --target ArduCopter.sitl`, we use `waf --target
ArduCopter` and the binary continues named as "ArduCopter.sitl".