[builtins] Introduce proper Float64Exp operator.

src/crankshaft/x64/lithium-x64.h

Index: src/crankshaft/x64/lithium-x64.h
diff --git a/src/crankshaft/x64/lithium-x64.h b/src/crankshaft/x64/lithium-x64.h
index 91f554137ac9d17c4e36f01ee74babfdfdadea7e..2ee0e4e6f9870eae1ba6afdcf8fdc51bd8a4289d 100644
--- a/src/crankshaft/x64/lithium-x64.h
+++ b/src/crankshaft/x64/lithium-x64.h
@@ -909,19 +909,11 @@ class LMathClz32 final : public LTemplateInstruction<1, 1, 0> {
   DECLARE_CONCRETE_INSTRUCTION(MathClz32, "math-clz32")
 };
 
-
-class LMathExp final : public LTemplateInstruction<1, 1, 2> {
+class LMathExp final : public LTemplateInstruction<1, 1, 0> {
  public:
-  LMathExp(LOperand* value, LOperand* temp1, LOperand* temp2) {
-    inputs_[0] = value;
-    temps_[0] = temp1;
-    temps_[1] = temp2;
-    ExternalReference::InitializeMathExpData();
-  }
+  explicit LMathExp(LOperand* value) { inputs_[0] = value; }
 
   LOperand* value() { return inputs_[0]; }
-  LOperand* temp1() { return temps_[0]; }
-  LOperand* temp2() { return temps_[1]; }
 
   DECLARE_CONCRETE_INSTRUCTION(MathExp, "math-exp")
 };