Hmm, I guess I must have missed some important flag or environment
variable when trying to reproduce it, sorry.
Given that IBM describes xlc as "legacy" (replaced by xlclang, but
still supported for some unspecified period of time for the benefit of
people who need C++ ABI compatibility with old code), I wonder how
long we plan to support it... Anecdotally, from a time 1-2 decades
ago when I used AIX daily, I can report that vast amounts of open
source stuff couldn't build with xlc, so gcc was used for pretty much
anything that didn't have a C++ ABI requirement. I kinda wonder if a
single person in the entire world appreciates that we support this.