Fix a misnomer.

Fix a misnomer.

* gettext-runtime/configure.ac: Prefer the term "shared library", since the term
"DLL" applies only to Windows.
* gettext-runtime/intl/configure.ac: Likewise.
* gettext-tools/configure.ac: Likewise.
* gettext-runtime/intl/export.h (LIBINTL_SHLIB_EXPORTED): Renamed from
LIBINTL_DLL_EXPORTED. Prefer the term "shared library", since the term "DLL"
applies only to Windows.
* gettext-runtime/intl/Makefile.am (AM_CPPFLAGS): Update comment.
(libgnuintl.h): Insert LIBINTL_SHLIB_EXPORTED instead of LIBINTL_DLL_EXPORTED.
* gettext-runtime/intl/gettextP.h: Use LIBGLOCALE_SHLIB_EXPORTED instead of
LIBGLOCALE_DLL_EXPORTED. Use LIBINTL_SHLIB_EXPORTED instead of
LIBINTL_DLL_EXPORTED.
* gettext-runtime/intl/loadinfo.h (LIBINTL_SHLIB_EXPORTED): Renamed from
LIBINTL_DLL_EXPORTED.
* gettext-runtime/intl/intl-compat.c (SHLIB_EXPORTED): Renamed from
DLL_EXPORTED. Prefer the term "shared library", since the term "DLL" applies
only to Windows.
* gettext-runtime/intl/printf.c (SHLIB_EXPORTED): Likewise.
* gettext-runtime/intl/setlocale.c (SHLIB_EXPORTED): Likewise.
* gettext-tools/woe32dll/export.h: Update comment.