acls: correct type/size for orig_umask

acls: correct type/size for orig_umask

Since 05278935 (- Call mkdir_defmode() instead of do_mkdir(). - Define
orig_umask in this file, not options.c. - Made orig_umask a mode_t, not an
int., 2006-02-24), the type for the global was changed, and therefore on
systems where sizeof(mode_t) != sizeof(int), writes or reads to them will
overflow to adjacent bytes.

Change the type to the one used everywhere else and avoid this problem.

While at it, silence again a warning that is being triggered by
Apple's clang 15.