[pmc2c] compile-time expand :optional and :opt_flag method args

still WIP, fails some tests:
t/pmc/class.t                             (Wstat: 0 Tests: 89 Failed: 9)
  Failed tests:  6-7, 13-16, 23-25
t/pmc/exporter.t                          (Wstat: 1024 Tests: 14 Failed: 4)
  Failed tests:  2-3, 5, 7
t/pmc/string.t                            (Wstat: 0 Tests: 160 Failed: 1)
  Failed test:  126