chown: avoid compilation warning on mingw * m4/chown.m4 (gl_FUNC_CHOWN): Recognize missing chown. * lib/chown.c (rpl_chown) [!HAVE_CHOWN]: Always return failure on mingw. * lib/lchown.c (lchown) [!HAVE_CHOWN]: Likewise. * modules/chown (Depends-on): Add errno. Signed-off-by: Eric Blake <ebb9@byu.net>