Move bionic_macros.h from private to platform.

Test: treehugger
Change-Id: Ie473914f4c8924c7240b3ac22093a9daf42fc948
diff --git a/libc/private/MallocXmlElem.h b/libc/private/MallocXmlElem.h
index a367972..f8c72ab 100644
--- a/libc/private/MallocXmlElem.h
+++ b/libc/private/MallocXmlElem.h
@@ -20,7 +20,7 @@
 #include <stdio.h>
 #include <unistd.h>
 
-#include <private/bionic_macros.h>
+#include <platform/bionic/macros.h>
 
 class MallocXmlElem {
  public: