user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/linux/generic/sys-reboot.cpp

@@ -0,0 +1,13 @@
+#include <errno.h>
+#include <sys/reboot.h>
+#include <bits/ensure.h>
+#include <mlibc/linux-sysdeps.hpp>
+
+int reboot(int what) {
+	MLIBC_CHECK_OR_ENOSYS(mlibc::sys_reboot, -1);
+	if (int e = mlibc::sys_reboot(what); e) {
+		errno = e;
+		return -1;
+	}
+	return 0;
+}