In configure, check for C++11
diff --git a/configure.ac b/configure.ac
index af7095e..27b0154 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,6 +6,7 @@
 AC_CONFIG_HEADERS([config.h])
 AC_PROG_CXX
 AC_LANG([C++])
+AX_CXX_COMPILE_STDCXX_11(, optional)
 
 AC_MSG_CHECKING([for std::shared_ptr])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(