[Bug c/88430] -Wmissing-attributes warnings when including libquadmath headers

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88430

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
The expected mechanism to apply the attributes is by using the new copy
attribute.  (It's been on my to-do list to look into these.)