enable C++11 if available

CMakeLists.txt

@@ -45,7 +45,7 @@ opt(CGNS "Enable CGNS mesh export (experimental)" OFF)
 opt(CAIRO "Enable Cairo to render fonts (experimental)" ${DEFAULT})
 opt(CHACO "Enable Chaco mesh partitioner (alternative to Metis)" ${DEFAULT})
 opt(COMPRESSED_IO "Enable compressed (gzip) input/output using zlib" OFF)
-opt(CXX11 "Compile with -std=c++11" OFF)
+opt(CXX11 "Enable C++11" ${DEFAULT})
 opt(DINTEGRATION "Enable discrete integration (needed for levelsets)" ${DEFAULT})
 opt(FLTK "Enable FLTK graphical user interface (requires mesh/post)" ${DEFAULT})
 opt(FOURIER_MODEL "Enable Fourier geometrical models (experimental)" OFF)
@@ -246,7 +246,11 @@ endif(ENABLE_OPENMP)
 
 if(ENABLE_CXX11)
   # in recent cmake versions we could do e.g. set(CMAKE_CXX_STANDARD 11)
+  check_cxx_compiler_flag("-std=c++11" STDCXX11)
+  if(STDCXX11)
+    set_config_option(HAVE_CXX11 "C++11")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+  endif(STDCXX11)
 endif(ENABLE_CXX11)
 
 macro(append_gmsh_src DIRNAME FILES)