[Bug libstdc++/71367] std::time_get does not implement 'r' or 'p'

[howard.hinnant at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71367

--- Comment #2 from Howard Hinnant <howard.hinnant at gmail dot com> ---
Just so this point doesn't go unnoticed, parsing should be case-insensitive.