Update LTO plugin interface

[Jan Hubicka]

> I'm also not sure what you mean by "resolved IRONLY except that it is
> externally visible to the dynamic linker." If we're building a shared
> library, and the symbol is exported, it's not going to be IRONLY, and
> I don't see how it would be valid to optimize it out. If we're

Well, the typical COMDAT symbols (ignoring side cases) needs to be put into
binary/library only if they are actually used, as all the other DSOs will define
them too if they are used there.
So it is valid to optimize out COMDAT after you optimized out all its uses. This
commonly happens at linktime.

Honza

> building an executable with --export-dynamic, same thing.
> 
> -cary