[UCRT] Use a C cast instead of const_cast for GCC

This is because GCC will generate errors for both const_cast and static_cast depending on the template parameter:
- With const_cast: error: invalid 'const_cast' from type 'std::nullptr_t' to type 'const wchar_t**'
- With static_cast: error: invalid 'static_cast' from type 'wchar_t** const' to type 'const wchar_t**'

sdk/lib/ucrt/inc/corecrt_internal_strtox.h

···
     EndPointer       const end
     ) throw()
 {
-    return c_string_character_source<Character>(string, const_cast<Character const**>(end));
+    return c_string_character_source<Character>(string, (Character const**)(end));
 }
 
 template <typename Integer, typename Character, typename EndPointer>