tests/pp/pp-def-7.c: add another macro recursion failing case

We do not mark a macro that should not be expanded further,
causing an incorrect additional expansion if used as an
argument.

RR2;
MM(RR2);

Should produce
  1 + RR2;
  1 + RR2;
but produces
  1 + RR2;
  1 + 1 + RR2;
tmp: Prepr: new approach to macro expansion