pthread_rwlock: use a mutex for process-private locks.

* instead of a benaphore.
* define PTHREAD_RWLOCK_INITIALIZER.
* adjust Init(), Destroy(), StructureLock() and StructureUnlock().

headers/posix/pthread.h

@@ -80,6 +80,8 @@ extern "C" {
 	{ PTHREAD_MUTEX_RECURSIVE, 0, -42, -1, 0 }
 #define PTHREAD_COND_INITIALIZER	\
 	{ 0, -42, NULL, 0, 0 }
+#define PTHREAD_RWLOCK_INITIALIZER	\
+	{ 0, -1, {{0}} }
 
 /* mutex functions */
 extern int pthread_mutex_destroy(pthread_mutex_t *mutex);

headers/posix/sys/types.h

@@ -105,15 +105,15 @@ struct _pthread_rwlock {
 	__haiku_std_int32	owner;
 	union {
 		struct {
-			__haiku_std_int32	sem;
-		} shared;
-		struct {
-			__haiku_std_int32	lock_sem;
-			__haiku_std_int32	lock_count;
+			__haiku_std_int32	mutex;
+			__haiku_std_int32	unused;
 			__haiku_std_int32	reader_count;
 			__haiku_std_int32	writer_count;
 			void*				waiters[2];
 		} local;
+		struct {
+			__haiku_std_int32	sem;
+		} shared;
 	} u;
 };