Implement all the POSIX _l functions.

Strictly speaking, this only implements the _l variants of the functions
we actually have. We're still missing nl_langinfo_l, for example, but we
don't have nl_langinfo either.

Change-Id: Ie711c7b04e7b9100932a13f5a5d5b28847eb4c12
Merge "Implement all the POSIX _l functions."