[Bug target/88529] G++ clears the return register on x86_64 when returning an empty class

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88529
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
related to PR20408 (but not the same as the patch which Jason attached is
different)