Pass multiboot magic and header to kmain

src/kernel/arch/x86/arch.zig

@@ -96,6 +96,13 @@ export nakedcc fn start_higher_half() noreturn {
         \\mov $KERNEL_STACK_END, %%esp
         \\mov %%esp, %%ebp
     );
+    // Push the bootloader magic number and multiboot header address with virtual offset
+    asm volatile (
+        \\.extern KERNEL_ADDR_OFFSET
+        \\push %%eax
+        \\add $KERNEL_ADDR_OFFSET, %%ebx
+        \\push %%ebx
+    );
     kmain();
     while (true) {}
 }