Fix missing function export.

Bug: 36401135

Test: Actually enable debug malloc and verify it loads properly.
Test: Ran unit tests.
(cherry picked from commit 2b0f2a48557ab2dd1171aa3ae79359ba44143a01)

Change-Id: I1e349554a8420fb763bf25ccebcb55d84a19eb0e
diff --git a/libc/malloc_debug/exported32.map b/libc/malloc_debug/exported32.map
index a985ef9..59bb102 100644
--- a/libc/malloc_debug/exported32.map
+++ b/libc/malloc_debug/exported32.map
@@ -13,6 +13,7 @@
     debug_malloc_disable;
     debug_malloc_enable;
     debug_malloc_usable_size;
+    debug_mallopt;
     debug_memalign;
     debug_posix_memalign;
     debug_pvalloc;
diff --git a/libc/malloc_debug/exported64.map b/libc/malloc_debug/exported64.map
index 1a6b30f..ec9d840 100644
--- a/libc/malloc_debug/exported64.map
+++ b/libc/malloc_debug/exported64.map
@@ -13,6 +13,7 @@
     debug_malloc_disable;
     debug_malloc_enable;
     debug_malloc_usable_size;
+    debug_mallopt;
     debug_memalign;
     debug_posix_memalign;
     debug_realloc;