Enforce C++-14 in 'CMakeLists.txt'

CMakeLists.txt

 cmake_minimum_required(VERSION 3.18)
-set(CXX_STANDARD 14)
+
+set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS  OFF)
 
 file(STRINGS "${CMAKE_SOURCE_DIR}/version.txt" version)
 
@@ -11,7 +14,7 @@ project(aidge_backend_opencv
 message(STATUS "Project name: ${CMAKE_PROJECT_NAME}")
 message(STATUS "Project version: ${version}")
 
-# Note : project name is {project} and python module name is also {project} 
+# Note : project name is {project} and python module name is also {project}
 set(module_name _${CMAKE_PROJECT_NAME}) # target name
 
 ##############################################
@@ -118,8 +121,8 @@ install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 install(EXPORT ${CMAKE_PROJECT_NAME}-targets
  FILE "${CMAKE_PROJECT_NAME}-targets.cmake"
  DESTINATION ${INSTALL_CONFIGDIR}
- COMPONENT ${module_name} 
-)  
+ COMPONENT ${module_name}
+)
 
 #Create a ConfigVersion.cmake file
 include(CMakePackageConfigHelpers)