[Bug c++/105584] libcxx needs using_if_exist attribute

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105584

--- Comment #7 from Sam James <sjames at gcc dot gnu.org> ---
Nor could they really be related if it's in libstdc++. Needs to be filed
separately.