add: gdt (peut etre y'a un gdt on sait pas)

headers/gdt.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+
+struct gdt_entry {
+    uint32_t limit;
+    uint32_t base;
+    uint8_t access_byte;
+    uint8_t flags;
+};
+
+// https://wiki.osdev.org/Global_Descriptor_Table#GDTR
+struct gdt_descriptor {
+    uint16_t size;
+    uint32_t base;
+} __attribute__((packed));
+
+void initGdt();