Export malloc_iterate and friends

Export malloc_iterate, malloc_enable, and malloc_disable to be used by
libmemunreachable.

Bug: 27208635
(cherry picked from commit 869691c6f7691dd5bf343617aa185c32e0d3d160)

Change-Id: Ifa44421a84ac3be6a57fac28c4da501febe88c28
diff --git a/libc/malloc_debug/exported64.map b/libc/malloc_debug/exported64.map
index 70fd581..8c47449 100644
--- a/libc/malloc_debug/exported64.map
+++ b/libc/malloc_debug/exported64.map
@@ -6,8 +6,11 @@
     debug_free_malloc_leak_info;
     debug_get_malloc_leak_info;
     debug_initialize;
+    debug_iterate;
     debug_mallinfo;
     debug_malloc;
+    debug_malloc_disable;
+    debug_malloc_enable;
     debug_malloc_usable_size;
     debug_memalign;
     debug_posix_memalign;