executor: apply optnone to guest_handle_nested_vmentry_intel()

Florent Revest reported ThinLTO builds failing with the following error:

  <inline asm>:2:1: error: symbol 'after_vmentry_label' is already defined
  after_vmentry_label:
  ^
  error: cannot compile inline asm

, which turned out to be caused by the compiler not respecting `noinline`.

Adding __attribute__((optnone)) fixes the problem.

Author: ramosian-glider

executor/common_kvm_amd64_syzos.h

@@ -1151,6 +1151,10 @@ guest_handle_nested_load_code(struct api_call_nested_load_code* cmd, uint64 cpu_
 	}
 }
 
+// Clang's LTO may ignore noinline and attempt to inline this function into both callers,
+// which results in duplicate declaration of after_vmentry_label.
+// __attribute__((optnone)) should prevent this behavior.
+__attribute__((optnone))
 GUEST_CODE static noinline void
 guest_handle_nested_vmentry_intel(uint64 vm_id, uint64 cpu_id, bool is_launch)
 {