Need an AC_TRY_LINK when checking for __thread in case a new gcc is combined with an old ld. (Bug 521750) r=bsmedberg

configure.in

@@ -4162,10 +4162,10 @@ fi
 
 AC_CACHE_CHECK(for __thread keyword for TLS variables,
                ac_cv_thread_keyword,
-               [AC_TRY_COMPILE([__thread bool tlsIsMainThread = false;],
-                               [return tlsIsMainThread;],
-                               ac_cv_thread_keyword=yes,
-                               ac_cv_thread_keyword=no)])
+               [AC_TRY_LINK([__thread bool tlsIsMainThread = false;],
+                            [return tlsIsMainThread;],
+                            ac_cv_thread_keyword=yes,
+                            ac_cv_thread_keyword=no)])
 if test "$ac_cv_thread_keyword" = yes; then
   AC_DEFINE(HAVE_THREAD_TLS_KEYWORD)
 fi