Implement GDT and basic IDT setup

This commit adds GDT initialization with proper code/data segments and reloads CS.

It also adds the initial IDT structure and loads an empty IDT.

Build configuration updated to disable SSE/MMX to prevent compiler generation of unsupported instructions in early boot.

src/CMakeLists.txt

@@ -2,6 +2,10 @@ cmake_minimum_required(VERSION 3.16)
 
 add_executable(kernel 
     boot.S
+    gdt_flush.S
+    gdt.c
+    idt.c
+    interrupts.S
     kernel.c
 )