[libstdc++] Make use of runtime demangler

[Benjamin Kosnik]

Sorry I slacked on this y'all. 

There is actually one sub directory of libstdc++-v3, libmath, that uses
config.h already. Basically, any of the "C" files can use it, and C++
files need c++config.h...

Sorry if this was not clear. 

I think Kaveh's patch is clearer, and also follows the rule that "C"
files can use config.h.

2002-05-03  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>

	* configure.in (AC_CHECK_HEADERS): Check for string.h & stdlib.h.
	* libsupc++/Makefile.am (LTCOMPILE): Add $(DEFS).

	* Makefile.in, config.h.in, configure: Regenerate.