[gold][patch] Add a add_input_library callback

[Rafael Espindola]

> Please make sure that http://gcc.gnu.org/wiki/whopr/driver is up to
> date with this and other changes, or get Cary to do it.  In
> particular, LDPT_ADD_INPUT_LIBRARY needs to be documented to explain
> what sort of file name should be passed--e.g., "c" to mean the same as
> "-lc".

I have updated the wiki. Let me know if you think I should change something.

> Thanks.
>
> Ian
>

Cheers,
-- 
Rafael Ávila de Espíndola