VS: Set CMAKE_VS_PLATFORM_NAME for VS7 and VS71 too

Move the code which sets CMAKE_VS_PLATFORM_NAME from
cmGlobalVisualStudio8Generator to cmGlobalVisualStudio7Generator.

Source/cmGlobalVisualStudio7Generator.h

@@ -36,9 +36,14 @@ public:
     return cmGlobalVisualStudio7Generator::GetActualName();}
   static const char* GetActualName() {return "Visual Studio 7";}
 
+  ///! Get the name for the platform.
+  const char* GetPlatformName() const;
+
   ///! Create a local generator appropriate to this Global Generator
   virtual cmLocalGenerator *CreateLocalGenerator();
 
+  virtual void AddPlatformDefinitions(cmMakefile* mf);
+
   /** Get the documentation entry for this generator.  */
   static void GetDocumentation(cmDocumentationEntry& entry);
 
@@ -153,6 +158,7 @@ protected:
   // Set during OutputSLNFile with the name of the current project.
   // There is one SLN file per project.
   std::string CurrentProject;
+  std::string PlatformName;
 };
 
 #define CMAKE_CHECK_BUILD_SYSTEM_TARGET "ZERO_CHECK"