[builtins] Introduce proper Float64Exp operator.

src/crankshaft/arm64/lithium-arm64.h

Index: src/crankshaft/arm64/lithium-arm64.h
diff --git a/src/crankshaft/arm64/lithium-arm64.h b/src/crankshaft/arm64/lithium-arm64.h
index 383e5c33c1c53dae81dd5969e954167a2c4ed5dc..98902434a9260f1ae68029e2bddaf882bf43aff1 100644
--- a/src/crankshaft/arm64/lithium-arm64.h
+++ b/src/crankshaft/arm64/lithium-arm64.h
@@ -1763,26 +1763,9 @@ class LMathAbsTagged: public LTemplateInstruction<1, 2, 3> {
   DECLARE_HYDROGEN_ACCESSOR(UnaryMathOperation)
 };
 
-
-class LMathExp final : public LUnaryMathOperation<4> {
+class LMathExp final : public LUnaryMathOperation<0> {
  public:
-  LMathExp(LOperand* value,
-                LOperand* double_temp1,
-                LOperand* temp1,
-                LOperand* temp2,
-                LOperand* temp3)
-      : LUnaryMathOperation<4>(value) {
-    temps_[0] = double_temp1;
-    temps_[1] = temp1;
-    temps_[2] = temp2;
-    temps_[3] = temp3;
-    ExternalReference::InitializeMathExpData();
-  }
-
-  LOperand* double_temp1() { return temps_[0]; }
-  LOperand* temp1() { return temps_[1]; }
-  LOperand* temp2() { return temps_[2]; }
-  LOperand* temp3() { return temps_[3]; }
+  explicit LMathExp(LOperand* value) : LUnaryMathOperation<0>(value) {}
 
   DECLARE_CONCRETE_INSTRUCTION(MathExp, "math-exp")
 };