common:w32: Don't expose unused functions.
* common/exechelp.h [HAVE_W32_SYSTEM] (get_max_fds): Don't expose. (close_all_fds, get_all_open_fds): Likewise. * common/exechelp-w32.c: Don't expose unused functions.
- GnuPG-bug-id: T7293
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>