libc function availability checker for a shared library

This script list up missing libc function called from a shared library.
Usage:
./scripts/check-libcfunc-avail.sh release apps/memcached/memcached.so

Signed-off-by: Takuya ASADA <syuu@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>