user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/tests/ansi/memmem.c

@@ -0,0 +1,24 @@
+#include <string.h>
+#include <assert.h>
+
+int main() {
+	char *haystack = "abc123\0x45";
+
+	char *needle1 = "abc";
+	void *rv = memmem(haystack, strlen(haystack), needle1, strlen(needle1));
+	assert(rv == haystack);
+
+	char *needle2 = "123";
+	rv = memmem(haystack, strlen(haystack), needle2, strlen(needle2));
+	assert(rv == haystack + 3);
+
+	char *needle3 = "1234";
+	rv = memmem(haystack, strlen(haystack), needle3, strlen(needle3));
+	assert(rv == NULL);
+
+	char *needle4 = "23\0x45";
+	rv = memmem(haystack, 10, needle4, 6);
+	assert(rv == haystack + 4);
+
+	return 0;
+}