configure.ac in rice-1.6.0 vs configure.ac in rice-1.6.1

@@ -19,9 +19,12 @@
   RICE_USING_MINGW32="true"
 else
   RICE_USING_MINGW32="false"
 fi
 
+m4_include(check_stdcxx_11.ac)
+AX_CXX_COMPILE_STDCXX_11(,optional)
+
 AC_SUBST(RICE_USING_MINGW32)
 
 m4_include(ruby.ac)
 RB_INIT_RUBY