COMP: require that we get compiled as C++11

This is required due to use of C++11 features,
such as `using` keyword instead of `typedef`.

Author: dzenanz

CMakeLists.txt

@@ -1,20 +1,21 @@
 cmake_minimum_required(VERSION 3.10.2)
 
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 11) # Supported values are ``11``, ``14``, and ``17``.
+endif()
+if(NOT CMAKE_CXX_STANDARD_REQUIRED)
+  set(CMAKE_CXX_STANDARD_REQUIRED ON)
+endif()
+if(NOT CMAKE_CXX_EXTENSIONS)
+  set(CMAKE_CXX_EXTENSIONS OFF)
+endif()
+
 ## If building external to ITK, we need to capture
 ## required build setting from ITK prior to calling
 ## project()
 if(NOT ITK_SOURCE_DIR)
   find_package(ITK REQUIRED)
   list(APPEND CMAKE_MODULE_PATH ${ITK_CMAKE_DIR})
-  if(NOT CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 11) # Supported values are ``11``, ``14``, and ``17``.
-  endif()
-  if(NOT CMAKE_CXX_STANDARD_REQUIRED)
-    set(CMAKE_CXX_STANDARD_REQUIRED ON)
-  endif()
-  if(NOT CMAKE_CXX_EXTENSIONS)
-    set(CMAKE_CXX_EXTENSIONS OFF)
-  endif()
 
   foreach(p
       ## Only policies introduced after the cmake_minimum_required