cmake: enforce c++ 11

CMakeLists.txt

@@ -120,9 +120,7 @@ endif()
 
 option(HPP_FCL_HAS_QHULL "use qhull library to compute convex hulls." FALSE)
 if(HPP_FCL_HAS_QHULL)
-  if(DEFINED CMAKE_CXX_STANDARD AND CMAKE_CXX_STANDARD EQUAL 98)
-    message(FATAL_ERROR "Cannot use qhull library with C++ < 11.\nYou may add -DCMAKE_CXX_STANDARD=11")
-  endif()
+  CHECK_MINIMAL_CXX_STANDARD(11 ENFORCE)
   find_package(Qhull COMPONENTS qhull_r qhullcpp)
   if(Qhull_FOUND)
     set(HPP_FCL_USE_SYSTEM_QHULL TRUE)