Note that the so-called "C" preprocessor actually neither knows nor cares anything about the syntax of 'C' - it is purely a text substitution & file inclusion processor.

Therefore, you can use the "C" preprocessor to pre-process any text file - including assembler source files, if you like.

Of course, it's not as powerful as Keil's Assembler macros - but it might help you...

I once worked on a project where the Linker script was generated using the 'C' preprocessor.