[Bug other/67304] Allow front-ends to share command-line options with different behaviours

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67304

--- Comment #4 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
I've just managed to have a brief time to think about this and look at how the
generator currently works, I think the following should be doable, and should
work with only one change to handle the fix-up of the opt index.

- Add a new flag called NoCombine.

- Options marked as such will not have flags or help combined in the code
generator, and be given a separate index in the options array after the
combined option itself.

- NoCombine should alias for the generated OPT_xxx enumeration.

- Back references should chain back to the original OPT_xxx entry in a linked
way, as the binary search in find_opt will guarantee that the last entry will
be matched first.

- The combined option should have all languages so that the diagnostic "is a
valid option for ..." references the correct frontends.

Example of generated code in options.h:

  OPT_J = 115,                               /* -J */
  /* OPT_J = 116, (CL_D) */                  /* -J */
  /* OPT_J = 117, (CL_Foo) */                /* -J */

And in options.c

  { "-J",
    "-J<directory>      Put MODULE files in 'directory'.",
    0,
    0,
    NULL, NULL, N_OPTS, N_OPTS, 1, -1,
    CL_D | CL_Foo | CL_Fortran | CL_JOINED | CL_SEPARATE,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    -1, 0, CLVC_STRING, 0 },
  { "-J",
    "-J <dir>   Look for string imports in <dir>",
    0,
    0,
    NULL, NULL, OPT_J, 115, 1, -1,
    CL_D | CL_JOINED | CL_SEPARATE | CL_NOCOMBINE,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    -1, 0, CLVC_STRING, 0 },
  { "-J",
    "Generate JSON file.",
    0,
    0,
    NULL, NULL, OPT_J, 116, 1, -1,
    CL_Foo | CL_NOCOMBINE,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    -1, 0, CLVC_BOOLEAN, 0 },