[Bug libstdc++/117630] Useless atexit entry for generic_category_instance and system_category_instance

[schwab--- via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117630

--- Comment #12 from Andreas Schwab <sch...@linux-m68k.org> ---
ld -M or ld --Map=file produces a map file that explains why an object is
needed.  There is also --cref.