user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/ansi/generic/uchar.cpp

@@ -0,0 +1,25 @@
+#include <bits/ensure.h>
+#include <uchar.h>
+#include <wchar.h>
+
+size_t c32rtomb(char *__restrict s, char32_t c32, mbstate_t *__restrict ps) {
+	return wcrtomb(s, c32, ps);
+}
+
+size_t mbrtoc32(char32_t *__restrict pc32, const char *__restrict pmb, size_t max, mbstate_t *__restrict ps) {
+	static mbstate_t internal_state;
+
+	if(!ps)
+		ps = &internal_state;
+
+	if(!pmb)
+		return mbrtoc32(nullptr, "", 1, ps);
+
+	wchar_t wc;
+	size_t ret = mbrtowc(&wc, pmb, max, ps);
+
+	if (ret <= 4 && pc32)
+		*pc32 = wc;
+
+	return ret;
+}