intl: Add support for per-thread locales on Solaris 11.4.

intl: Add support for per-thread locales on Solaris 11.4.

Relies on the recent changes to the 'localename' module in gnulib.

* gettext-runtime/intl/localename.c: Apply changes from gnulib.
* gettext-runtime/intl/localename-table.h: New file, from gnulib.
* gettext-runtime/intl/localename-table.c: New file, from gnulib.
* gettext-runtime/intl/libgnuintl.in.h (newlocale, duplocale, freelocale): New
overriding declarations.
* gettext-runtime/intl/Makefile.in (HEADERS): Add localename-table.h.
(SOURCES): Add localename-table.c.
(OBJECTS): Add localename-table.$lo.
(localename-table.lo): New target.
(libgnuintl.h, libintl.h): Substitute also HAVE_NAMELESS_LOCALES.
* gettext-runtime/m4/intl.m4: Apply changes from gnulib:
(gt_INTL_SUBDIR_CORE): Don't test for 'uselocale' and 'getlocalename_l'.
Instead, invoke gt_INTL_SOLARIS. Set HAVE_NAMELESS_LOCALES.
* gettext-runtime/m4/intlsolaris.m4: New file, from gnulib.
* gettext-runtime/m4/Makefile.am (EXTRA_DIST): Add it.
* gettext-tools/m4/Makefile.am (aclocal_DATA): Add intlsolaris.m4.
* gettext-tools/misc/gettextize.in (m4filelist): Add intlsolaris.m4.
* Makefile.am (distcheck-hook): Verify that intlsolaris.m4 is consistent with
gnulib.
* gettext-tools/doc/gettext.texi (aclocal): Add intlsolaris.m4 to the file list.
* PACKAGING: Add intlsolaris.m4 to the list of installed files.
* NEWS: Mention the change.