Remove unnecessary includes of v8 headers from platform files

src/codegen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 95 matching lines @@
 
   static bool RecordPositions(MacroAssembler* masm,
                               int pos,
                               bool right_here = false);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CodeGenerator);
 };
 
 
-// Results of the library implementation of transcendental functions may differ
-// from the one we use in our generated code.  Therefore we use the same
-// generated code both in runtime and compiled code.
-typedef double (*UnaryMathFunction)(double x);
-
-UnaryMathFunction CreateExpFunction();
-UnaryMathFunction CreateSqrtFunction();
-
-
 class ElementsTransitionGenerator : public AllStatic {
  public:
   // If |mode| is set to DONT_TRACK_ALLOCATION_SITE,
   // |allocation_memento_found| may be NULL.
   static void GenerateMapChangeElementsTransition(MacroAssembler* masm,
       AllocationSiteMode mode,
       Label* allocation_memento_found);
   static void GenerateSmiToDouble(MacroAssembler* masm,
                                   AllocationSiteMode mode,
                                   Label* fail);
   static void GenerateDoubleToObject(MacroAssembler* masm,
                                      AllocationSiteMode mode,
                                      Label* fail);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ElementsTransitionGenerator);
 };
 
 static const int kNumberDictionaryProbes = 4;
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_CODEGEN_H_