Add and use public.libraries.buildbot.txt file.

Needed after the latest NativeLoader changes.

Change-Id: Ia80ebe85ccfc702470eebe6daa9d675abcf8014d
diff --git a/tools/public.libraries.buildbot.txt b/tools/public.libraries.buildbot.txt
new file mode 100644
index 0000000..6251da3
--- /dev/null
+++ b/tools/public.libraries.buildbot.txt
@@ -0,0 +1,3 @@
+libc.so
+libdl.so
+libm.so