The pre-processor of an assembler is specific to that very assembler.

For instance, with a C pre-processor, I have a very lean C pre-processor dialect which allows me to assemble simple x86_64 code with... fasmg[12] or nasm(probably yasm) or gas(intel syntax).

A big project which was bitten by specific pre-processor abuse: ffmpeg with nasm (but it is still much less toxic than to start to be hard dependent on advanced and specific C compiler extensions... look a the failure from linux on that matter).