strerror_r: fix Solaris test failures Solaris 10 populates buf on EINVAL, but not on ERANGE. * lib/strerror_r.c (strerror_r): Partially populate buf on ERANGE failures. * doc/posix-functions/strerror_r.texi (strerror_r): Document this. Signed-off-by: Eric Blake <eblake@redhat.com>