Fixes Android build by using C++ math header instead of C one.

runtime/lib/double.cc

Index: runtime/lib/double.cc
===================================================================
--- runtime/lib/double.cc	(revision 37827)
+++ runtime/lib/double.cc	(working copy)
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#include <math.h>
+#include <cmath>
 
 #include "vm/bootstrap_natives.h"
 
@@ -73,7 +73,7 @@
 
 
 static RawInteger* DoubleToInteger(double val, const char* error_msg) {
-  if (isinf(val) || isnan(val)) {
+  if (std::isinf(val) || std::isnan(val)) {
     const Array& args = Array::Handle(Array::New(1));
     args.SetAt(0, String::Handle(String::New(error_msg)));
     Exceptions::ThrowByType(Exceptions::kUnsupported, args);
@@ -258,13 +258,13 @@
 
 DEFINE_NATIVE_ENTRY(Double_getIsInfinite, 1) {
   const Double& arg = Double::CheckedHandle(arguments->NativeArgAt(0));
-  return Bool::Get(isinf(arg.value())).raw();
+  return Bool::Get(std::isinf(arg.value())).raw();
 }
 
 
 DEFINE_NATIVE_ENTRY(Double_getIsNaN, 1) {
   const Double& arg = Double::CheckedHandle(arguments->NativeArgAt(0));
-  return Bool::Get(isnan(arg.value())).raw();
+  return Bool::Get(std::isnan(arg.value())).raw();
 }
 
 
@@ -272,7 +272,7 @@
   const Double& arg = Double::CheckedHandle(arguments->NativeArgAt(0));
   // Include negative zero, infinity.
   double dval = arg.value();
-  return Bool::Get(signbit(dval) && !isnan(dval)).raw();
+  return Bool::Get(std::signbit(dval) && !std::isnan(dval)).raw();
 }
 
 // Add here only functions using/referring to old-style casts.