(where empty string arg to newlocale, per SUSv4, means "an implementation-
defined native environment.  This correspons to the value of the associated
environment variables, LC_* and LANG") instead of relying on whatever setlocale
would be in effect here.

Also, nl_langinfo_l is less of an MT nightmare than nl_langinfo, which is of
benefit once the last remaining use of nl_langinfo in sal/osl/unx/nlsupport.cxx
will also have been changed to nl_langinfo_l.

loplugin:nullptr needs a little hack, as SUSv4 locale_t could be anything from
an integer type to a pointer type.

Change-Id: Ic35dcbc2e0a4f650694b48df12470dd89476dff5