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..d4c142190a418a4460c84cd60e483b20d997f1c2 100644
--- a/src/untrusted/pthread/pthread_types.h
+++ b/src/untrusted/pthread/pthread_types.h
@@ -47,11 +47,12 @@ struct __nc_basic_thread_data;
  *       ("tcbhead_t") as long as we keep the field "dtv" untouched and
  *       use tls_base in a compatible way (which we already do).
  */
-typedef struct {
+typedef struct nc_thread_descriptor {
   void *tls_base;  /* tls accesses are made relative to this base */
   void *unused_dtv;  /* increase compatibility with glibc's tcbhead_t */
   int joinable;
   int join_waiting;
+  unsigned int rdlock_count;  /* number of rdlocks this thread holds */
   nc_thread_memory_block_t *stack_node;
   nc_thread_memory_block_t *tls_node;
   nc_thread_function start_func;