Mark undef flag functions as memory(none), nounwind, willreturn

This allows for dead store elimination of the flags

src/striga/semantics.py

@@ -133,10 +133,17 @@ class Semantics:
         self.call_handler = self.module.add_function("__striga_call", helper_ty)
         self.ret_handler = self.module.add_function("__striga_ret", helper_ty)
         self.syscall_handler = self.module.add_function("__striga_syscall", helper_ty)
-        self.undef_flags = {
-            name: self.module.add_function(f"__striga_undef_{name}", undef_flag_ty)
-            for name in FLAGS
-        }
+        def add_undef_flag_helper(name: str) -> Function:
+            helper = self.module.add_function(f"__striga_undef_{name}", undef_flag_ty)
+            # Undefined-flag helpers model arbitrary values, not side effects.
+            # Match Remill's symbolic/undefined helper annotations so calls can
+            # be deleted after their flag stores are proven dead.
+            helper.attributes.add_memory("none")
+            helper.attributes.add("nounwind")
+            helper.attributes.add("willreturn")
+            return helper
+
+        self.undef_flags = {name: add_undef_flag_helper(name) for name in FLAGS}
 
         # Set per function lifted
         self.insn_blocks: dict[int, BasicBlock] = {}