PATCH: 2 stage BFD linker for LTO plugin

[Ian Lance Taylor]

Richard Guenther <richard.guenther@gmail.com> writes:

> Nice.  Can we on the GCC side somehow identify Gold versions
> that support this and avoid -pass-through handling in that case?

Sure.  The LDPT_GOLD_VERSION tag, which lto-plugin currently ignores,
will return the version of gold.  I can bump that version when I commit
this patch, and lto-plugin can check it.

> I'm not sure if with your patch the add_input_library or
> add_input_file plugin hooks are completely useless (and thus
> gold could simply ignore those at all).

The plugin does need to use the add_input_file callback.  In any case
I'm not sure it's a great idea for gold to ignore a hook, there might be
some need for it in the future.

Ian