[lto] Add support for running execute.exp with -flto

[William Maddox]

On 10/19/07, Diego Novillo <dnovillo@google.com> wrote:

> I was wrong.  I got confused by my script that always puts -flto in
> the gcc call.  The LTO behaviour is *only* done if -flto is given in
> the final link command.

This is the specified behavior, and is "the right thing", as the ".o"
files produced by LTO also contain ordinary object code, and could
reasonably be linked in the normal way, without LTO.

--Bill