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_detach.cpp b/libc/bionic/pthread_detach.cpp
index fb8e0dd..011e6c6 100644
--- a/libc/bionic/pthread_detach.cpp
+++ b/libc/bionic/pthread_detach.cpp
@@ -29,8 +29,10 @@
 #include <errno.h>
 #include <pthread.h>
 
+#include "private/bionic_defs.h"
 #include "pthread_internal.h"
 
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
 int pthread_detach(pthread_t t) {
   pthread_internal_t* thread = __pthread_internal_find(t);
   if (thread == NULL) {