[Bug libstdc++/116531] Forward declaration with std::vector does not compile with -O on arm

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116531

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
> only for arm (an EABI difference?)

Constructors return "this" for arm eabi (note aarch64 follows the original ia64
c++ abi here).