weak for Darwin

[Benjamin Kosnik]

This is the right idea, however the default should be to do nothing, and
config/os/darwin/os_defines.h should define _GLIBCXX_WEAK_DEFINITION to
do the special stuff.

-benjamin

>2004-11-01  Aaron W. LaFramboise <aaronavay62@aaronwl.com>
>
>	* config/os/mingw32/os_defines.h
>	(_GLIBCXX_WEAK_DEFINITION): Define.
>	* include/bits/c++config (_GLIBCXX_WEAK_DEFINITION): Define.
>	* libsupc++/del_op.cc (operator delete(void *)): Use
>	_GLIBCXX_WEAK_DEFINITION.
>	* libsupc++/del_opnt.cc
>	(operator delete(void *, const std::nothrow_t&): Same.
>	* libsupc++/del_opv.cc (operator delete[](void *)): Same.
>	* libsupc++/del_opvnt.cc
>	(operator delete[](void *, const std::nothrow_t&): Same.
>	* libsupc++/new_op.cc (operator new(std::size_t)): Same.
>	* libsupc++/new_opnt.cc
>	(operator new(std::size_t, const std::nothrow_t&)): Same
>	* libsupc++/new_opv.cc (operator new[](std::size_t)): Same.
>	* libsupc++/new_opvnt.cc
>	(operator new[](std::size_t, const std::nothrow_t&)): Same.