[libc++] Redirect strftime_l to the locale-ignorant strftime on mingw

[mstorsjo]

Summary

_strftime_l is only available in the numbered msvcrt versions (starting from msvcr80.dll). In the default configuration, mingw targets the unversioned msvcrt.dll - and there, _strftime_l is not available (not even on windows 10).

If MSVCRT_VERSION is set to a higher value (indicating a non-default target and wanting to link to msvcrXX.dll), use the correct function.

[compnerd]

ick

include/support/win32/locale_win32.h

 #define iswupper_l _iswupper_l
 #define iswlower_l _iswlower_l
 #define iswalpha_l _iswalpha_l
 #define iswdigit_l _iswdigit_l
 #define iswpunct_l _iswpunct_l
 #define iswxdigit_l _iswxdigit_l
 #define towupper_l _towupper_l
 #define towlower_l _towlower_l
+#if defined(__MINGW32__) && __MSVCRT_VERSION__ < 0x0800
+#define strftime_l( __s, __l, __f, __tm, __loc ) strftime( __s, __l, __f, __tm )
+#else
 #define strftime_l _strftime_l
+#endif
 #define sscanf_l( __s, __l, __f, ...) _sscanf_l( __s, __f, __l, __VA_ARGS__ )
 #define vsscanf_l( __s, __l, __f, ...) _sscanf_l( __s, __f, __l, __VA_ARGS__ )
 #define sprintf_l( __s, __l, __f, ... ) _sprintf_l( __s, __f, __l, __VA_ARGS__ )
 #define vsprintf_l( __s, __l, __f, ... ) _vsprintf_l( __s, __f, __l, __VA_ARGS__ )
 #define vsnprintf_l( __s, __n, __l, __f, ... ) _vsnprintf_l( __s, __n, __f, __l, __VA_ARGS__ )
 _LIBCPP_FUNC_VIS int snprintf_l(char *ret, size_t n, locale_t loc, const char *format, ...);
 _LIBCPP_FUNC_VIS int asprintf_l( char **ret, locale_t loc, const char *format, ... );
 _LIBCPP_FUNC_VIS int vasprintf_l( char **ret, locale_t loc, const char *format, va_list ap );