[turol]

> In theory it should only be about writing a new build script (not based on `wmake` but on a real `make`). And then workout the tiny flag/preprocessor/C compiler discrepancies.

For mostly C code like the original Doom source, yes. But it looks like FastDoom people have added quite a bit of assembly. That needs to be ported to AT&T syntax. Or you need to find out if Intel syntax works in your version of DJGPP's gas. While this should work nowadays I have not tried it. Then there's other differences like Watcom mapping low memory by default into the low part of the address space but DJGPP needing explicit mapping or access.