Here are some tools that have been verified to work on Linux and/or Windows 7. Some of them are DOS tools which can run under DOSBox.

Assembly:  A86 (DOSBox),  MASM (DOSBox),  NASM (Linux/Windows 7),  as86 (Linux), emu8086 (Windows 7)

C/C++:   Open Watcom (Windows 7),  bcc (Linux)

My preference is to write in assembly code and use A86 to generate a .COM file which I can simply copy into the FPGA code ROM.