[csa] Add Unreachable() and use it after throw sites

src/builtins/builtins-string.cc

Index: src/builtins/builtins-string.cc
diff --git a/src/builtins/builtins-string.cc b/src/builtins/builtins-string.cc
index d3fae3764f8165f0936e23468224f4fd5add66d6..b1103d3a62b8a95fde97ac684cec18a2fbb64476 100644
--- a/src/builtins/builtins-string.cc
+++ b/src/builtins/builtins-string.cc
@@ -1906,12 +1906,11 @@ TF_BUILTIN(StringIteratorPrototypeNext, StringBuiltinsAssembler) {
   Bind(&throw_bad_receiver);
   {
     // The {receiver} is not a valid JSGeneratorObject.
-    Node* result =
-        CallRuntime(Runtime::kThrowIncompatibleMethodReceiver, context,
-                    HeapConstant(factory()->NewStringFromAsciiChecked(
-                        "String Iterator.prototype.next", TENURED)),
-                    iterator);
-    Return(result);  // Never reached.
+    CallRuntime(Runtime::kThrowIncompatibleMethodReceiver, context,
+                HeapConstant(factory()->NewStringFromAsciiChecked(
+                    "String Iterator.prototype.next", TENURED)),
+                iterator);
+    Unreachable();
   }
 }