[libstdc++] Make use of runtime demangler

[Kaveh R. Ghazi]

 > From: Franz Sirl <Franz.Sirl-kernel@lauterbach.com>
 > 
 > Kaveh, do you really need the extra check for stdlib.h on your platform? On 
 > Linux the stuff in acinclude handles that, so only a new check for string.h 
 > is missing.

No.  I didn't really need stdlib.h, only string.h is explicitly
necessary once the DEFS were set appropriately.  However I found that
libstdc++-v3's configure was very convoluted and felt better listing
both with a comment explaining why they were necessary was more clear.
At worst you'd pull it from cache for subsequent queries.

But I'm not married to my approach.  If your patch works then I'll
hold off checking in mine.  If it fixes the implicit decls on linux,
then I'm sure it'll do so on solaris and irix.  There was nothing
platform specific about my patch.

		--Kaveh
--
Kaveh R. Ghazi			Director of Systems Architecture
ghazi@caip.rutgers.edu		Qwest Global Services