user: implement mlibc as the libc, finally.

It's finally done..

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

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

@@ -0,0 +1,12 @@
+#include <stdlib.h>
+#include <wchar.h>
+#include <assert.h>
+#include <string.h>
+
+int main() {
+	const wchar_t str[] = L"wcsrtombs";
+	const wchar_t *p = str;
+	int ret = wcsrtombs(NULL, &p, 343245234, NULL);
+	assert(ret == 9);
+	return 0;
+}