Mark __BIONIC_WEAK_FOR_NATIVE_BRIDGE symbols

To make it easier for Native Bridge implementations
to override these symbols.

Bug: http://b/67993967
Test: make
Change-Id: I4c53e53af494bca365dd2b3305ab0ccc2b23ba44
diff --git a/libc/bionic/pthread_join.cpp b/libc/bionic/pthread_join.cpp
index 4d852cb..be76c20 100644
--- a/libc/bionic/pthread_join.cpp
+++ b/libc/bionic/pthread_join.cpp
@@ -28,9 +28,11 @@
 
 #include <errno.h>
 
+#include "private/bionic_defs.h"
 #include "private/bionic_futex.h"
 #include "pthread_internal.h"
 
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
 int pthread_join(pthread_t t, void** return_value) {
   if (t == pthread_self()) {
     return EDEADLK;