Define NOTHREADS to 1 if thread_local keyword is not available

configure.ac

@@ -197,6 +197,21 @@ std::vector<std::future<int>> v;
     [have_std_future=no
      AC_MSG_RESULT([no])])
 
+# Check that thread_local is available.
+AC_MSG_CHECKING([whether thread_local is available])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[[
+]],
+[[
+thread_local int n;
+]])],
+    [AC_DEFINE([HAVE_THREAD_LOCAL], [1],
+               [Define to 1 if you have the `thread_local`.])
+     have_thread_local=yes
+     AC_MSG_RESULT([yes])],
+    [have_thread_local=no
+     AC_MSG_RESULT([no])])
+
 # Check that std::map::emplace is available for g++-4.7.
 AC_MSG_CHECKING([whether std::map::emplace is available])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
@@ -608,9 +623,13 @@ if test "x$debug" != "xno"; then
     AC_DEFINE([DEBUGBUILD], [1], [Define to 1 to enable debug output.])
 fi
 
-# Some platform does not have working std::future.  We disable
-# threading for those platforms to exclude std::future use.
-if test "x$threads" != "xyes" || test "x$have_std_future" != "xyes"; then
+enable_threads=yes
+# Some platform does not have working std::future or thread_local.  We
+# disable threading for those platforms.
+if test "x$threads" != "xyes" ||
+   test "x$have_std_future" != "xyes" ||
+   test "x$have_thread_local" != "xyes"; then
+    enable_threads=no
     AC_DEFINE([NOTHREADS], [1], [Define to 1 if you want to disable threads.])
 fi
 
@@ -698,4 +717,5 @@ AC_MSG_NOTICE([summary of build options:
       Libnghttp2_asio:${enable_asio_lib}
       Examples:       ${enable_examples}
       Python bindings:${enable_python_bindings}
+      Threading:      ${enable_threads}
 ])