https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94168
--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- The reasoning for rejecting this (for UCNs in both C and C++, for other characters in C++ because of the C++ rule that such characters get converted to UCNs) is that the constraints on permitted characters in identifiers appear to me to apply to any pp-token that matches the syntax productions for "identifier", whether or not that pp-token ends up getting converted to a token. This is similar to #if 0 "multiline string" #endif being disallowed as well.
