[Bug translation/79643] Please define the file format of *.opt files more i18n-friendly

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79643

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Well, it could have been -m[no-]custom=X,Y,... instead of separate options, but
yes, it's hard to improve this as requested.