fix nl_langinfo with static linking (BZ #16915)

For static linking the locale code avoids linking code and data for
unused categories. However for nl_langinfo we know only at runtime which
categories are used, so direct reference to every nl_current_CATEGORY
symbol should be done.

This was broken by commit bc3e1c12 where
nl_langinfo_l and nl_langinfo have been merged and some code has been
lost in the process.

In order to detect locales issues with static linking, compile a version
of tst-langinfo with static linking.

Note: this is Debian bug#747103 reported by Raphael <raphael.astier@eliot-sa.com>