[Bug middle-end/41455] memcpy not tail called if it's a struct assignment

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41455

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect what we can do is "lower" assignments to memcpy in a pass right
before tail call to optimize this case.