https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106840
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It is treated as an extension even for C and older C++.
But given the discussions Joseph started, the above patch changes it such that
it only will be recognized as an extension outside of string/character literals
if it starts with \N{ rather than just \N and only in the non-standard modes
(-std=gnu*) except for -std=c++2{3,b}.
So \NARG will be handled as before without any diagnostics...
