Implement Math.log1p using port from fdlibm.

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);
 
 // Constants to be exposed to builtins via Float64Array.
-struct TrigonometricConstants {
-  static const double constants[34];
+struct MathConstants {
+  static const double constants[45];
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_FDLIBM_H_