[builtins] Introduce proper Float64Exp operator.

src/crankshaft/arm/lithium-codegen-arm.cc

Index: src/crankshaft/arm/lithium-codegen-arm.cc
diff --git a/src/crankshaft/arm/lithium-codegen-arm.cc b/src/crankshaft/arm/lithium-codegen-arm.cc
index 8eda5922f428547bfe55c7e7c5f11c07447bf94e..65ad7107e1c8b81daacab29e49a748bef8cf26c2 100644
--- a/src/crankshaft/arm/lithium-codegen-arm.cc
+++ b/src/crankshaft/arm/lithium-codegen-arm.cc
@@ -3540,16 +3540,10 @@ void LCodeGen::DoPower(LPower* instr) {
 
 
 void LCodeGen::DoMathExp(LMathExp* instr) {
-  DwVfpRegister input = ToDoubleRegister(instr->value());
-  DwVfpRegister result = ToDoubleRegister(instr->result());
-  DwVfpRegister double_scratch1 = ToDoubleRegister(instr->double_temp());
-  DwVfpRegister double_scratch2 = double_scratch0();
-  Register temp1 = ToRegister(instr->temp1());
-  Register temp2 = ToRegister(instr->temp2());
-
-  MathExpGenerator::EmitMathExp(
-      masm(), input, result, double_scratch1, double_scratch2,
-      temp1, temp2, scratch0());
+  __ PrepareCallCFunction(0, 1, scratch0());
+  __ MovToFloatParameter(ToDoubleRegister(instr->value()));
+  __ CallCFunction(ExternalReference::ieee754_exp_function(isolate()), 0, 1);
+  __ MovFromFloatResult(ToDoubleRegister(instr->result()));
 }