[builtins] Introduce proper Float64Tan operator.

src/third_party/fdlibm/fdlibm.h

-// The following is adapted from fdlibm (http://www.netlib.org/fdlibm).
-//
-// ====================================================
-// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
-//
-// Developed at SunSoft, a Sun Microsystems, Inc. business.
-// Permission to use, copy, modify, and distribute this
-// software is freely granted, provided that this notice
-// is preserved.
-// ====================================================
-//
-// The original source code covered by the above license above has been
-// modified significantly by Google Inc.
-// Copyright 2014 the V8 project authors. All rights reserved.
-
-#ifndef V8_FDLIBM_H_
-#define V8_FDLIBM_H_
-
-namespace v8 {
-namespace fdlibm {
-
-int rempio2(double x, double* y);
-
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_FDLIBM_H_