cmExportInstallFileGenerator: Allow overriding of CheckInterfaceDirs

Source/cmExportInstallFileGenerator.h

@@ -135,6 +135,10 @@ protected:
                                 ImportPropertyMap& properties,
                                 std::set<std::string>& importedLocations);
 
+  virtual bool CheckInterfaceDirs(std::string const& prepro,
+                                  cmGeneratorTarget const* target,
+                                  std::string const& prop) const;
+
   cmInstallExportGenerator* IEGen;
 
   // The import file generated for each configuration.
@@ -145,9 +149,6 @@ protected:
   std::map<std::string, std::vector<std::string>> ConfigCxxModuleTargetFiles;
 
 private:
-  bool CheckInterfaceDirs(std::string const& prepro,
-                          cmGeneratorTarget const* target,
-                          std::string const& prop) const;
   void PopulateCompatibleInterfaceProperties(cmGeneratorTarget const* target,
                                              ImportPropertyMap& properties);
   void PopulateCustomTransitiveInterfaceProperties(