Implement pthread_rwlock functions for NaCl newlib.

src/untrusted/pthread/pthread_types.h

Index: src/untrusted/pthread/pthread_types.h
diff --git a/src/untrusted/pthread/pthread_types.h b/src/untrusted/pthread/pthread_types.h
index df587815c4a58896bd0cebd883304a9844dbe11a..26beaea4ffa392791c58f73ab2720c478b2730a4 100644
--- a/src/untrusted/pthread/pthread_types.h
+++ b/src/untrusted/pthread/pthread_types.h
@@ -52,6 +52,7 @@ typedef struct {
   void *unused_dtv;  /* increase compatibility with glibc's tcbhead_t */
   int joinable;
   int join_waiting;
+  int rdlock_count;  /* how many rdlock's does this thread hold */

[Mark Seaborn, 2015/02/02 18:29:13]

Nit: remove apostrophe.

How about writing this as a noun phrase rather than a question: "number of
rdlocks this thread holds"

Also:

 * You need to initialise this field in nc_thread.c.

 * "unsigned" would be preferred to avoid undefined behaviour in the event of an
overflow.

[Sam Clegg, 2015/02/02 19:25:08]

Done.

   nc_thread_memory_block_t *stack_node;
   nc_thread_memory_block_t *tls_node;
   nc_thread_function start_func;