[v3] add missing dg-require to tests

[Jonathan Wakely]

http://gcc.gnu.org/ml/gcc-testresults/2011-10/msg02603.html shows two
test failures on sparc64-linux, fixed by this patch.

Tested x86_64-linux and committed to trunk.

        * testsuite/30_threads/async/49668.cc: Add missing dg-require.
        * testsuite/30_threads/packaged_task/49668.cc: Likewise.

Index: testsuite/30_threads/async/49668.cc
===================================================================
--- testsuite/30_threads/async/49668.cc (revision 180359)
+++ testsuite/30_threads/async/49668.cc (working copy)
@@ -4,6 +4,7 @@
 // { dg-options " -std=gnu++0x " { target *-*-cygwin *-*-darwin* } }
 // { dg-require-cstdint "" }
 // { dg-require-gthreads "" }
+// { dg-require-atomic-builtins "" }
 
 // Copyright (C) 2011 Free Software Foundation, Inc.
 //
Index: testsuite/30_threads/packaged_task/49668.cc
===================================================================
--- testsuite/30_threads/packaged_task/49668.cc (revision 180359)
+++ testsuite/30_threads/packaged_task/49668.cc (working copy)
@@ -4,6 +4,7 @@
 // { dg-options " -std=gnu++0x " { target *-*-cygwin *-*-darwin* } }
 // { dg-require-cstdint "" }
 // { dg-require-gthreads "" }
+// { dg-require-atomic-builtins "" }
 
 // Copyright (C) 2011 Free Software Foundation, Inc.
 //