mariadb-native: fix link error on Ubuntu 13.10

Below errors only occurs on Ubuntu 13.10:

$arch-linux-libtool: link: g++ ... -o .libs/mysqltest_embedded \
    ../../libmysqld/.libs/libmysqld.so -ldl

    ../../libmysqld/.libs/libmysqld.so: undefined reference to `dlopen'
    ../../libmysqld/.libs/libmysqld.so: undefined reference to `dlclose'
    ../../libmysqld/.libs/libmysqld.so: undefined reference to `dlerror'
    ../../libmysqld/.libs/libmysqld.so: undefined reference to `dlsym'

GCC/ld verion on the host:
    gcc (Ubuntu/Linaro 4.8.1-10ubuntu8) 4.8.1
    GNU ld (GNU Binutils for Ubuntu) 2.23.52.20130913

This is a strange behavior on Ub13.10, it fails even '-ldl' in the
link command line. This patch will append '-ldl' to dependency_libs
in libmysqld.la.

Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>