Enhance: c++11 support check when using CMake.

CMakeLists.txt

@@ -2,7 +2,17 @@ cmake_minimum_required(VERSION 2.8)
 project (easypr)
 
 # c++11 required
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+include(CheckCXXCompilerFlag)
+CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
+CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
+
+if(COMPILER_SUPPORTS_CXX11)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+elseif(COMPILER_SUPPORTS_CXX0X)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
+else()
+    message(STATUS "The compiler ${CMAKE_CXX_COMPILER} doesn’t support C++11. Please upgrade or use a different C++ compiler.")
+endif()
 
 # opencv package required
 find_package(OpenCV REQUIRED)