Expose per-process memory init.

In order to disable memory initialization for a process, the following
command can be used:

    android_mallopt(M_DISABLE_MEMORY_MITIGATIONS, nullptr, 0);

Since this is needed in vendor processes, this is exposing this
functionality to llndk. For convenience (and adding standard logging),
a helper function is being added into libcutils in order to use this,
w/o having to get into so many details.

Bug: 166675194
Test: use function from libcutils
Change-Id: Ia816089a9f3469c50c70afaa7244abeac5a51dcd
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 64f583a..a17a33f 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1476,8 +1476,8 @@
     # Used by libandroid_net
     android_getaddrinfofornet; # apex
 
-    # Used by libandroid_runtime, libmedia and libmediautils
-    android_mallopt; # apex
+    # Used by libandroid_runtime, libcutils, libmedia, and libmediautils
+    android_mallopt; # apex llndk
 } LIBC_P;
 
 LIBC_R { # introduced=R