kassert: Explicitly include <sys/_types>

[olce]

Summary

Including it is needed to have '__va_list' defined.

This is a step to make <sys/kassert.h> usable without the need to
explicitly include other headers.

[imp]

title should likely say _types.h though.
And do you still need cdefs.h, since _types.h already does? style(9) says types.h, but maybe we need to update that too?

[markj]

In D49972#1140034, @imp wrote:

title should likely say _types.h though.
And do you still need cdefs.h, since _types.h already does? style(9) says types.h, but maybe we need to update that too?

I could have sworn that style.9 says that one can assume that param.h and (_)types.h include cdefs.h, but I can't find any mention of that.

IMO it's okay to drop the cdefs include, but it doesn't matter much here.