Allow sysroots to be relocated under $prefix as well as $exec_prefix

[Mark Mitchell]

Richard Sandiford wrote:

>> I think the GCC part is sufficiently obvious, or else ping Paolo.
> 
> I think "obvious" is a bit of a stretch in this case, so I'll hold
> off the applying until the gcc part is reviewed.

The GCC bits are OK, assuming no objections from a build system
maintainer within 24 hours.

Thanks,

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713