Add first C user program

src/kernel/idt.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+struct interrupt_frame {
+  uint64_t ip;
+  uint64_t cs;
+  uint64_t flags;
+  uint64_t sp;
+  uint64_t ss;
+};
+
+void idt_init();
+
+void idt_set_entry(int vector, void (*handler)(struct interrupt_frame *), uint8_t flags);