[Bug libstdc++/86843] Allow separating debug mode into ABI-changing part and rest

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86843

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh I think I misread it ... it does enable some internal assertions, but is
mostly the same meaning as our debug mode.