PPC/s390: [crankshaft] Refactor kAllowUndefinedAsNaN to kTruncatingToNumber.

src/crankshaft/s390/lithium-s390.h

Index: src/crankshaft/s390/lithium-s390.h
diff --git a/src/crankshaft/s390/lithium-s390.h b/src/crankshaft/s390/lithium-s390.h
index 45b5d6b248710736d9b39896fe3d654028cd1c5a..b946d4f271c8a65483d874f6700248067c27f8a2 100644
--- a/src/crankshaft/s390/lithium-s390.h
+++ b/src/crankshaft/s390/lithium-s390.h
@@ -1697,6 +1697,8 @@ class LNumberUntagD final : public LTemplateInstruction<1, 1, 0> {
 
   DECLARE_CONCRETE_INSTRUCTION(NumberUntagD, "double-untag")
   DECLARE_HYDROGEN_ACCESSOR(Change)
+
+  bool truncating() { return hydrogen()->CanTruncateToNumber(); }
 };
 
 class LSmiUntag final : public LTemplateInstruction<1, 1, 0> {