I've been using the FPCUpDeluxe install of the crosscompiler, which ships with crosslibs for Linux, so I can compile regular GUI programs fine. The problem is that I'm trying to link to SDL2. On Windows it's fine since the DLL doesn't need to be there at linktime, but (as I learned from this thread) on Linux the .so does. How nice.
I installed libsdl2-dev on an Ubuntu VM and copied it over to my Windows machine, but it started referencing other .so files which ended up being sort of a rabbit hole.
I'm going to try compiling SDL2 from source with fewer features enabled (I just need the audio capabilities) and see what I can do.
Initially I tried to just compile on Linux directly, however the program is 32 bit and it's damn near impossible to get FPC to compile a 32 bit binary on Linux.