cmLocalUnixMakefileGenerator3: Mark GetRelativeTargetDirectory const

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -809,7 +809,7 @@ void cmLocalUnixMakefileGenerator3::WriteConvenienceRule(
 }
 
 std::string cmLocalUnixMakefileGenerator3::GetRelativeTargetDirectory(
-  cmGeneratorTarget* target)
+  cmGeneratorTarget const* target) const
 {
   std::string dir =
     cmStrCat(this->HomeRelativeOutputPath, this->GetTargetDirectory(target));

Source/cmLocalUnixMakefileGenerator3.h

@@ -139,7 +139,8 @@ public:
   void WriteSpecialTargetsTop(std::ostream& makefileStream);
   void WriteSpecialTargetsBottom(std::ostream& makefileStream);
 
-  std::string GetRelativeTargetDirectory(cmGeneratorTarget* target);
+  std::string GetRelativeTargetDirectory(
+    cmGeneratorTarget const* target) const;
 
   // File pairs for implicit dependency scanning.  The key of the map
   // is the depender and the value is the explicit dependee.