vndk-def: Add NDK extension usages check

This commit adds extra checks to make sure vendor modules do not depend
on extended symbols from NDK libs.

Test: Add a new function to libc and run check-dep command with
--aosp-system option and "depends on NDK extended symbol" shows up.

Change-Id: Ic4cfdb97201307359b47eb46d79ce13e8f2580f6