Fix constness of accessors.

Source/cmGeneratorExpressionDAGChecker.cxx

@@ -153,7 +153,7 @@ bool cmGeneratorExpressionDAGChecker::EvaluatingLinkLibraries()
 }
 
 //----------------------------------------------------------------------------
-bool cmGeneratorExpressionDAGChecker::EvaluatingIncludeDirectories()
+bool cmGeneratorExpressionDAGChecker::EvaluatingIncludeDirectories() const
 {
   const char *prop = this->Property.c_str();
   return (strcmp(prop, "INCLUDE_DIRECTORIES") == 0
@@ -161,7 +161,7 @@ bool cmGeneratorExpressionDAGChecker::EvaluatingIncludeDirectories()
 }
 
 //----------------------------------------------------------------------------
-bool cmGeneratorExpressionDAGChecker::EvaluatingCompileDefinitions()
+bool cmGeneratorExpressionDAGChecker::EvaluatingCompileDefinitions() const
 {
   const char *prop = this->Property.c_str();
   return (strcmp(prop, "COMPILE_DEFINITIONS") == 0

Source/cmGeneratorExpressionDAGChecker.h

@@ -38,8 +38,8 @@ struct cmGeneratorExpressionDAGChecker
                    const std::string &expr);
 
   bool EvaluatingLinkLibraries();
-  bool EvaluatingIncludeDirectories();
-  bool EvaluatingCompileDefinitions();
+  bool EvaluatingIncludeDirectories() const;
+  bool EvaluatingCompileDefinitions() const;
 
 private:
   Result checkGraph() const;