Introduce first cut of struct _thr_locale_t used for the locale_t definition.
Introduce global instance called __global_locale used by default.
Introduce internal inline functions __get_global_locale, __get_locale_r,
__get_current_locale.
Remove usage of global variables in favor of accessor functions pointing to
__global_locale for now. Include all local headers in locale subdir from
setlocale.h to get single include for internal locale access.
Introduce __CTYPE_PTR macro to replace direct access to __ctype_ptr__
and use throughout in isxxx functions.
Signed-off by: Corinna Vinschen <corinna@vinschen.de>