Temporarily avoid PPC64 LE bootstrap by making GLIBC_2.17 and GLIBC_2.18 equivalent.

[Adam Conrad]

On Fri, Jan 31, 2014 at 09:44:12AM +0100, Andreas Jaeger wrote:
> 
> Thanks a lot Carlos for this! This should make much life easier for all
> of us if there's a change,

Ditto from me.  I suspect Andreas and I are both still in the "please
don't force us to rebuild everything" camp, but this hack is very much
appreciated (and much shorter and cleaner than the first hack that came
to mind when I was pondering this), so thanks in advance for making our
lives less awful if we need it.

... Adam