@ MiiNiPaa: There is literally no reason it shouldn't.
@ OP: There is some file duplication involved, and you need a separate installer for each platform you support, which you would need to have in some form or another anyway. But honestly you can scratch out everything I said about makefile, you'd be hard pressed to find a more flexible solution then that.
It depends. If you statically link all of the required libraries (or if there are no libraries required at all), then yes. Otherwise, no. You'd have to ship the dynamic libraries with it.
Sorry about this, not too good with the law system for software.
Neither are the people writing it. Yes, GPL is one of the licenses that allows you to redistribute the product that it is attached to. http://www.gnu.org/copyleft/gpl.html