jit_ocaml: more type checking
jit_ocaml: cleanup of C files

* Remove C files and headers (jit_ocaml.c -> scicaml_stubs.cpp)
jit_ocaml: remove useless flags from OCaml AST
Fix include without ifdefs
jit_ocaml: modified runvisitors to call the OCaml interpreter instead
  of the C++ interpreter