ref: ec4c79f3a6ed97ec0c407a870827382cbefb1166
dir: /src/libc/string/strstr.c/
#include <stddef.h>
#include <string.h>
#undef strstr
char *
strstr(const char *s1, const char *s2)
{
	const char *p;
	int c = *s2;
	int len;
	if ((len = strlen(s2)) == 0)
		return s1;
	for (p = s1; p = strchr(p, c); ++p) {
		if (!strncmp(p, s2, len))
			return p;
	}
	return NULL;
}