gold patch to discard .note.callgraph sections in the final link.

[Cary Coutant]

> As I understand it, SHF_EXCLUDE sections should not be discarded by an
> ld -r link.  If gold is doing that today, which it probably is, that
> should be fixed.  So, yeah, SHF_EXCLUDE sounds like a much better way to
> deal with this.

Sounds good to me. Now we either need an assembly syntax for
SHF_EXCLUDE, or Sri will need to add his section to the list of
special cases in special_sections[] in bfd/elf.c.

-cary