Patch to libstc++: Remove strdup from locale_facets.tcc

[Benjamin Kosnik]

> a) __convert_from_v must not use setlocale but uselocale for GLIBC 2.3+.

right.

> b) is "C" locale really the right one to use, or should it use the
>    const __c_locale& argument?

The "C" locale is correct, given the way the input strings are formatted
currently.

> a) is further complicated by lack of __uselocale prototype, so I'm afraid
>    we might need the:
>    namespace __gnu_cxx_loc {
>      extern "C" __typeof(uselocale) __uselocale;
>    }
>    ...
>    and use __gnu_cxx_loc::__uselocale()

Just use __gnu_cxx if this is necessary.

-benjamin