X87: [crankshaft] Refactor kAllowUndefinedAsNaN to kTruncatingToNumber.

src/crankshaft/x87/lithium-x87.h

Index: src/crankshaft/x87/lithium-x87.h
diff --git a/src/crankshaft/x87/lithium-x87.h b/src/crankshaft/x87/lithium-x87.h
index 623e3410a4f38aea098386558bd6c3233c1af9d2..3653a2de2f14b9b07e4a77c2b787fe34d0d1f0b2 100644
--- a/src/crankshaft/x87/lithium-x87.h
+++ b/src/crankshaft/x87/lithium-x87.h
@@ -1871,6 +1871,8 @@ class LNumberUntagD final : public LTemplateInstruction<1, 1, 1> {
 
   DECLARE_CONCRETE_INSTRUCTION(NumberUntagD, "double-untag")
   DECLARE_HYDROGEN_ACCESSOR(Change);
+
+  bool truncating() { return hydrogen()->CanTruncateToNumber(); }
 };