Leave more space for extensions in pthread_rwlockattr_t

Change pthread_rwlockattr_t from int to long. On LP64 this gives us more
room for extensibility since longs are 8 bytes. glibc also reserves 8
bytes for this.

Bug: 14582681
Bug: 12875898
Change-Id: I55d599be0fdbbf0cb55957ec0ea62ab042bdee94
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 3f59b91..7b8de81 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -91,7 +91,7 @@
 typedef long pthread_mutexattr_t;
 typedef long pthread_condattr_t;
 
-typedef int pthread_rwlockattr_t;
+typedef long pthread_rwlockattr_t;
 
 typedef struct {
   pthread_mutex_t lock;