For AROS, I use whatever build system that AROS project is using.
For classic Amiga OS, I use whatever compiler the project I am hacking on was written for, typically under UAE for speed. And likewise, for Linux/m68k I build natively but under emulator, in this case Aranym (and soon Qemu, maybe).
MorphOS and OS4 are of little interest, but I am not a developer as much as I am someone who happily tinker with existing code in attempts to make it do what I want
