I suggest looking at LinuxFromScratch[0], especially II.5. It's hard to do a "real" cross-platform compiler because your target system might not only be a different architecture but also has different libraries on the system with which the compiler has to work. All in all, doing it right and being able to ship binaries is a lot of work and constant maintenance as your target system, in this case Raspbian, also changes their libraries.

[0] http://www.linuxfromscratch.org/lfs/view/stable/