cmMakefile: Extract an accessor for the global generator.

Both for convenience, and because cmMakefile should not be the
way to get access to the local generator, so that should go away
in the future.

Source/cmMakefile.cxx

@@ -3693,7 +3693,12 @@ bool cmMakefile::GetIsSourceFileTryCompile() const
 
 cmake *cmMakefile::GetCMakeInstance() const
 {
-  return this->LocalGenerator->GetGlobalGenerator()->GetCMakeInstance();
+  return this->GetGlobalGenerator()->GetCMakeInstance();
+}
+
+cmGlobalGenerator* cmMakefile::GetGlobalGenerator() const
+{
+  return this->LocalGenerator->GetGlobalGenerator();
 }
 
 #ifdef CMAKE_BUILD_WITH_CMAKE

Source/cmMakefile.h

@@ -712,6 +712,7 @@ public:
    * Get the instance
    */
   cmake *GetCMakeInstance() const;
+  cmGlobalGenerator* GetGlobalGenerator() const;
 
   /**
    * Get all the source files this makefile knows about