This is another case which changed from compile time undefined behavior
to ill-formed, diagnostic required. Now, we warn on this, so pedantically
that is good enough, maybe all we need is a testcase, but the following
patch changes it to a pedwarn for C++26.
2025-08-04 Jakub Jelinek <jakub@redhat.com>
PR preprocessor/120778
* macro.cc (stringify_arg): For C++26 emit a pedarn instead of warning
for \ at the end of stringification.
* g++.dg/DRs/dr2578.C: New test.
b9f443b617