[wwwdocs] Add info about IPA optimization and LTO improvments

[Gerald Pfeifer]

On Wed, 28 Sep 2011, Andi Kleen wrote:
> <li>ld -r is now supported with LTO. When using assembler files or non 
> LTOed objects inside ld -r objects together with LTO then the Linux 
> binutils 2.21.51.0.3 or later are needed.</li>

I think this should be GNU/Linux, if anything, but then I also think
we should not refer to this $notsurewhatthepropertermis variant of our 
official binutils project as part of GCC release notes.

Gerald