ref: 0fd54eed0f32a4ea1a91111ceffe23e08fc1d2ee
dir: /sys/src/ape/lib/ap/gen/strncat.c/
#include <string.h>
char*
strncat(char *s1, const char *s2, size_t n)
{
	char *os1;
	long nn;
	os1 = s1;
	nn = n;
	while(*s1++)
		;
	s1--;
	while(*s1++ = *s2++)
		if(--nn < 0) {
			s1[-1] = 0;
			break;
		}
	return os1;
}