-dc -dparse don't work for clightgen

[bcip]

I am working on my own copy but there should be the same issue in master branch. When using clightgen, flags -dc and -dparse don't have any actual effect. The following modification should fix this problem.

In compile_c_file of exportclight/Clightgen.ml, add the following lines:

let set_dest dst opt ext =
    dst := if !opt then Some (output_filename sourcename ".c" ext)
      else None in
  set_dest Cprint.destination option_dparse ".parsed.c";
  set_dest PrintCsyntax.destination option_dcmedium ".compcert.c";
  set_dest PrintClight.destination option_dclight ".light.c";

[bschommer]

Should be fixed by commit 1574cf2.