[cxx0x_compiler.m4]

Try -std=c++11 before -std=c++0x as the latter causes a warning for
Clang. (solves partly FS#989)

[[Imported from SVN: r6986]]

m4/cxx0x_compiler.m4

-# whether g++ accepts -std=c++0x
+# whether compiler accepts -std=c++11 or -std=c++0x
+# can be disabled by --disable-gxx0xcheck
 
 AC_DEFUN([GXX0X],[
   ac_save_CXX="$CXX"
-  AC_CACHE_CHECK([whether g++ accepts -std=c++0x], dune_cv_gplusplus_accepts_cplusplus0x, [
+  
+  # try flag -std=c++11
+  AC_CACHE_CHECK([whether $CXX accepts -std=c++11], dune_cv_gplusplus_accepts_cplusplus11, [
     AC_REQUIRE([AC_PROG_CXX])
     AC_ARG_ENABLE(gxx0xcheck,
       AC_HELP_STRING([--disable-gxx0xcheck],
-        [try to enable c++0x feature for g++ [[default=yes]]]),
+        [try flag -std=c++11 to enable C++11 features [[default=yes]]]),
         [gxx0xcheck=$enableval],
         [gxx0xcheck=yes])
     if test "x$GXX" = xyes && test "x$gxx0xcheck" = xyes; then
       AC_LANG_PUSH([C++])
-      CXX="$CXX -std=c++0x"
+      CXX="$CXX -std=c++11"
       AC_TRY_COMPILE([
         #include <iostream>
         #include <array>
         ], [],
-        dune_cv_gplusplus_accepts_cplusplus0x=yes,
-        dune_cv_gplusplus_accepts_cplusplus0x=no)
-      AC_LANG_POP
+        dune_cv_gplusplus_accepts_cplusplus11=yes,
+        dune_cv_gplusplus_accepts_cplusplus11=no)
+      AC_LANG_POP([C++])
     fi
   ])
-  if test "x$dune_cv_gplusplus_accepts_cplusplus0x" == "xyes" ; then
-    CXX="$ac_save_CXX -std=c++0x"
-    CXXCPP="$CXXCPP -std=c++0x"
+  if test "x$dune_cv_gplusplus_accepts_cplusplus11" == "xyes" ; then
+    CXX="$ac_save_CXX -std=c++11"
+    CXXCPP="$CXXCPP -std=c++11"
   else
     CXX="$ac_save_CXX"
+    
+    # try flag -std=c++0x instead
+    AC_CACHE_CHECK([whether $CXX accepts -std=c++0x], dune_cv_gplusplus_accepts_cplusplus0x, [
+      AC_REQUIRE([AC_PROG_CXX])
+      AC_ARG_ENABLE(gxx0xcheck,
+        AC_HELP_STRING([--disable-gxx0xcheck],
+          [try flag -std=c++0x to enable C++11 features [[default=yes]]]),
+          [gxx0xcheck=$enableval],
+          [gxx0xcheck=yes])
+      if test "x$GXX" = xyes && test "x$gxx0xcheck" = xyes; then
+        AC_LANG_PUSH([C++])
+        CXX="$CXX -std=c++0x"
+        AC_TRY_COMPILE([
+          #include <iostream>
+          #include <array>
+          ], [],
+          dune_cv_gplusplus_accepts_cplusplus0x=yes,
+          dune_cv_gplusplus_accepts_cplusplus0x=no)
+        AC_LANG_POP([C++])
+      fi
+    ])
+    if test "x$dune_cv_gplusplus_accepts_cplusplus0x" == "xyes" ; then
+      CXX="$ac_save_CXX -std=c++0x"
+      CXXCPP="$CXXCPP -std=c++0x"
+    else
+      CXX="$ac_save_CXX"
+    fi
   fi
 ])