PATCH: Fix libstdc++ testsuite on systems without ranlib

[Paolo Carlini]

Hi,
> Not yet, but irrespective of the needs of IRIX 5, there is a bug here:
> the libstdc++ testsuite expects to find AR and RANLIB in the
> environment, only falling back to hardcoded values if they are missing,
> and they are not passed.  This is obviously wrong.
>   
I can certainly trust you here, still I'm a bit scared by such kind of
change at this stage in the release process, where, as far as I know,
nobody else has noticed problems for all the other targets we support.
Let's see what Paolo thinks, as build system maintainer, he decides if
this is really urgent for 4.5.0 or should wait for 4.6.0.

Paolo.