Add mallopt to canonical list of exports.

Bug: 62202823

Test: Ran script and verified that none of the other map files are modified.
Change-Id: Ib890ce77c60b877434fbb65a5add8f6c4603d3d0
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index f05e7eb..c453a38 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1579,4 +1579,5 @@
     malloc_disable;
     malloc_enable;
     malloc_iterate;
+    mallopt;
 } LIBC_O;