I was able to do that with GNU Make. Granted, the syntax is a bit ... odd, but it was doable.

    ASM = A09/a09

    %.o %.l : %.a
            $(ASM) -o $(*F).o -l $(*F).l $(*F).a

    clean:
            /bin/rm -rf *.o *.l

    foo : disasm.l
    bar : disasm.o
    baz : disasm.l disasm.o

The target baz has both a .l and a .o, both of which are produced in one command. The line that begins with "%.o" starts an implicit rule, which loosely states, in English: "to produce a .o file, or a .l file, run the following ...". $(*F) is a GNUism that maps to the filename of the source (directory part, if any, is stripped). This works. I tested all three targets (foo, bar, baz) with a "make clean" between each one.

(and for the really curious, a09 is a 6809 assembler; disasm.a is a 6809 diassembler, written in 6809; binary is a 2K relocatable library)