Add more tests for t-printf and t-strerror.

* tests/t-printf.c (check_fwrite): New.
(main): Add check_fwrite.
* tests/t-strerror.c (main): Add three more cases to LIST.

The string in check_fwrite is from the Gateless Gate, for
people who want to discuss "Niente". --- gniibe

• Co-authored-by: NIIBE Yutaka <gniibe@fsij.org>
• Signed-off-by: "pengyi" <pengyi37@huawei.com>