Implement pthread_rwlock functions for NaCl newlib.

tests/threads/nacl.scons

Index: tests/threads/nacl.scons
diff --git a/tests/threads/nacl.scons b/tests/threads/nacl.scons
index bc28b8b91f4977eb17974633b944b3beb7a167a6..995d5c105308a0d7d0872b58b2e9fea47c829dd3 100644
--- a/tests/threads/nacl.scons
+++ b/tests/threads/nacl.scons
@@ -150,6 +150,19 @@ env.AddNodeToTestSuite(node, ['small_tests'], 'run_mutex_timedlock_test',
                        is_broken=env.IsRunningUnderValgrind() or
                                  env.UsingEmulator())
 
+rwlock_test_nexe = env.ComponentProgram(
+    'rwlock_test',
+    ['rwlock_test.c'],
+    EXTRA_LIBS=['${PTHREAD_LIBS}', '${NONIRT_LIBS}'])
+
+node = env.CommandSelLdrTestNacl(
+    'rwlock_test.out',
+    rwlock_test_nexe
+    )
+env.AddNodeToTestSuite(node, ['small_tests'], 'run_rwlock_test',
+                       is_broken=env.IsRunningUnderValgrind() or
+                                 env.UsingEmulator())
+
 thread_stack_test_nexe = env.ComponentProgram('thread_stack_test',
                                               'thread_stack_test.c',
                                               EXTRA_LIBS=['${PTHREAD_LIBS}',