fix C++11 detection

scripts/ax_cxx_compile_stdcxx_11.m4

@@ -201,15 +201,17 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX_14], [dnl
       AC_MSG_ERROR([*** A compiler with support for C++14 language features is required.])
     fi
   else
-    HAVE_CXX11=${HAVE_CXX14}
     if test x$ac_success = xno; then
       HAVE_CXX14=0
       AC_MSG_NOTICE([No compiler with C++14 support was found])
       AX_CXX_COMPILE_STDCXX_11([$1], [optional])
     else
+      HAVE_CXX11=1
       HAVE_CXX14=1
       AC_DEFINE(HAVE_CXX14,1,
                 [define if the compiler supports basic C++14 syntax])
+      AC_DEFINE(HAVE_CXX11,1,
+                [define if the compiler supports basic C++14 syntax])
     fi
     AC_SUBST(HAVE_CXX11)
     AC_SUBST(HAVE_CXX14)