Make bionic_malloc.h a platform header.

Instead of having platform directories directly include the
private header, create a platform header directory and export it.

Bug: 130763340

Test: Builds.
Change-Id: Ie0f092b3fe077a3de8b90266c0b28bfbc20d0dfa
Merged-In: Ie0f092b3fe077a3de8b90266c0b28bfbc20d0dfa
(cherry picked from commit 8f582ef2f8a77d953d0e9f33387f592d20f852e2)
diff --git a/libc/malloc_hooks/tests/malloc_hooks_tests.cpp b/libc/malloc_hooks/tests/malloc_hooks_tests.cpp
index 86e20ea..1858781 100644
--- a/libc/malloc_hooks/tests/malloc_hooks_tests.cpp
+++ b/libc/malloc_hooks/tests/malloc_hooks_tests.cpp
@@ -38,7 +38,7 @@
 
 #include <gtest/gtest.h>
 
-#include <private/bionic_malloc.h>
+#include <bionic/malloc.h>
 #include <private/bionic_malloc_dispatch.h>
 #include <tests/utils.h>