Build timestamp prevents reproducible builds [0].
Thanks to the debian project for the patch.

[0] https://reproducible-builds.org/docs/timestamps/

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

Add missing `limits.h` and `sys/types.h` includes to the appropriate
source files.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>