[PATCH, libstdc++-v3] Fix import of wide character related symbols in stdlib.h wraper

[Jonathan Wakely]

On 26/01/16 06:40 +0200, Andris Pavenis wrote:
>include/c_compatibility/stdlib.h imports wide character related symbols
>into global namespace unconditionaly which causes libstdc++-v3 build
>to fail when one or both of _GLIBCXX_USE_WCHAR_T and _GLIBCXX_HAVE_MBSTATE_T
>are not defined.
>
>Included patch changes it to import them into global namespace only
>when they are defined in cstdlib

OK for trunk, thanks.