Move bionic_macros.h from private to platform.

Test: treehugger
Change-Id: Ie473914f4c8924c7240b3ac22093a9daf42fc948
diff --git a/libc/bionic/pthread_atfork.cpp b/libc/bionic/pthread_atfork.cpp
index fb12a3b..0dcabdf 100644
--- a/libc/bionic/pthread_atfork.cpp
+++ b/libc/bionic/pthread_atfork.cpp
@@ -30,7 +30,7 @@
 #include <pthread.h>
 #include <stdlib.h>
 
-#include "private/bionic_macros.h"
+#include "platform/bionic/macros.h"
 
 struct atfork_t {
   atfork_t* next;