intl: Fix support for per-thread locales on Solaris 11.4.
* gettext-runtime/intl/localename-table.in.h: Renamed from
gettext-runtime/intl/localename-table.h.
* gettext-runtime/intl/Makefile.in (HEADERS): Add localename-table.in.h. Remove
localename-table.h.
(localename-table.h): New target.
(localename.$lo, localename-table.$lo): Update dependencies.
(mostlyclean): Remove localename-table.h.