cmake: should detect c++11 before enabling it

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 33f7ae95487436e8206dd6f9430d5b69693e70a5..c90e2ed7952c5a2f9e555557c97e0a792f46f5f5 100644 (file)
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -123,14 +123,15 @@ endif(no_yasm)
 if(CMAKE_VERSION VERSION_LESS "3.1")
   include(CheckCXXCompilerFlag)
   CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
-  if(COMPILER_SUPPORTS_CXX11)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
-  else()
-    message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support.")
+  if(NOT COMPILER_SUPPORTS_CXX11)
+    message(FATAL_ERROR
+      "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support.")
   endif()
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 else()
   set(CMAKE_CXX_STANDARD 11)
   set(CMAKE_CXX_EXTENSIONS OFF)
+  set(CMAKE_CXX_STANDARD_REQUIRED ON)
 endif()
 
 ## Handle diagnostics color if compiler supports them.