Making sure that the TestingExternal projects can be build with install tree

Change-Id: I5a4f75ea6dad676d80d75eba00ff86d713624938

CMake/VTKConfig.cmake.in

@@ -37,6 +37,9 @@ endif()
 # Load module interface macros.
 include("@VTK_CONFIG_MODULE_API_FILE@")
 
+# Load testing interface macros.
+include("@VTK_CONFIG_TESTING_MACROS_FILE@")
+
 # Compute set of requested modules.
 if(VTK_FIND_COMPONENTS)
   # Specific modules requested by find_package(VTK).

CMake/vtkModuleTop.cmake

@@ -274,6 +274,8 @@ set(VTK_CONFIG_CMAKE_DIR "${VTK_SOURCE_DIR}/CMake")
 set(VTK_CONFIG_TARGETS_CONDITION " AND NOT VTK_BINARY_DIR")
 set(VTK_CONFIG_TARGETS_FILE "${VTK_BINARY_DIR}/VTKTargets.cmake")
 set(VTK_CONFIG_MODULE_API_FILE "${VTK_SOURCE_DIR}/CMake/vtkModuleAPI.cmake")
+set(VTK_CONFIG_TESTING_MACROS_FILE "${VTK_SOURCE_DIR}/CMake/vtkTestingMacros.cmake")
+
 # Target used to ensure VTKConfig is load just once
 set(VTK_COMMON_TARGET vtkCommonCore)
 configure_file(CMake/VTKConfig.cmake.in VTKConfig.cmake @ONLY)