selftests/nolibc: add new gettimeofday test cases

These 2 test cases are added to cover the normal using scenes of
gettimeofday().

They have been used to trigger and fix up such issue with nolibc:

    nolibc-test.c:(.text.gettimeofday+0x54): undefined reference to `__aeabi_ldivmod'

This issue happens while there is no "unsigned int" conversion in the
coming new clock_gettime / clock_gettime64 syscall path of
gettimeofday():

    tv->tv_usec = ts.tv_nsec / 1000;

Suggested-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/linux-riscv/280867a8-7601-4a96-9b85-87668e1f1282@t-8ch.de/


Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>