selftests/nolibc: fix up int_fast16/32_t test cases for musl

musl limits the fast signed int in 32bit, but glibc and nolibc don't, to
let such test cases work on musl, let's provide the type based
SINT_MAX_OF_TYPE(type) and SINT_MIN_OF_TYPE(type).

Suggested-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/bc635c4f-67fe-4e86-bfdf-bcb4879b928d@t-8ch.de/


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