[Bug lto/48200] Implement function attribute for symbol versioning (.symver)

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48200

--- Comment #40 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I posted initial patch here
https://gcc.gnu.org/ml/gcc-patches/2019-11/msg01334.html