PREVAILING_DEF_IRONLY_EXP

[Cary Coutant]

> Why is PREVAILING_DEF_IRONLY_EXP needed?
> ...
> Is there a case I am missing? Maybe a symbol that is defined in comdat in
> one file but can have an undefined reference without accompanying definition
> in another!?! If not, I would propose changing the text to

This is pretty much the reason. We want to distinguish between symbols
that are truly referenced from outside the IR and those that are
merely exported, so that the compiler can only drop the optimized-away
symbols without assuming that all code in the app was produced by that
compiler, using the same conventions.

See:

   http://sourceware.org/ml/binutils/2010-12/msg00040.html

and follow-ups for the reasoning.

-cary