Implement pthread_rwlock functions for NaCl newlib

src/untrusted/pthread/pthread_internal.h

Index: src/untrusted/pthread/pthread_internal.h
diff --git a/src/untrusted/pthread/pthread_internal.h b/src/untrusted/pthread/pthread_internal.h
index d15b86175c352de78c18808f0b06d2ff03559eed..eae8ce70bef8f2b33ff3ca6b872da18e3f110558 100644
--- a/src/untrusted/pthread/pthread_internal.h
+++ b/src/untrusted/pthread/pthread_internal.h
@@ -8,9 +8,12 @@
 #define NATIVE_CLIENT_SRC_UNTRUSTED_PTHREAD_PTHREAD_INTERNAL_H_ 1
 
 #include "native_client/src/untrusted/irt/irt.h"
+#include "native_client/src/untrusted/nacl/tls.h"
+#include "native_client/src/untrusted/nacl/tls_params.h"
 #include "native_client/src/untrusted/pthread/pthread.h"
+#include "native_client/src/untrusted/pthread/pthread_types.h"
 
-struct nc_combined_tdb;
+#define TDB_SIZE (sizeof(struct nc_combined_tdb))
 
 extern int __nc_thread_initialized;
 extern pthread_t __nc_initial_thread_id;
@@ -23,4 +26,14 @@ void __nc_initialize_interfaces(void);
 
 void __nc_tsd_exit(void);
 
+static inline struct nc_thread_descriptor *__nc_get_tdb(void) {
+  /*
+   * Fetch the thread-specific data pointer.  This is usually just
+   * a wrapper around __libnacl_irt_tls.tls_get() but we don't use
+   * that here so that the IRT build can override the definition.
+   */
+  return (void *) ((char *) __nacl_read_tp_inline()
+                   + __nacl_tp_tdb_offset(TDB_SIZE));
+}
+
 #endif