Windows: Workaround a UTF-8 issue in Gettext's libintl_setlocale()

See the comment. In this package, locale is set at program startup and
not changed later, so the point (2) in the comment isn't a problem.

Fixes: 46ee006162
(cherry picked from commit b40e3321a7fb9dfdf8ffb30e7e0788c2f0abc941)

src/common/tuklib_gettext.h

@@ -24,6 +24,57 @@
 #endif
 
 #if TUKLIB_GETTEXT
+#	if defined(_WIN32) && !defined(__CYGWIN__)
+		// <libintl.h> from gettext-runtime redirects setlocale()
+		// to libintl_setlocale(). As of gettext 0.22.5 (and probably
+		// 0.23), libintl_setlocale(LC_ALL, "") doesn't set the locale
+		// to UTF-8 if UTF-8 code page has been set in the application
+		// manifest. For example, one may get "fi_FI" when native
+		// setlocale() would result in "Finnish_Finland.utf8". The
+		// lack of ".utf8" (or equivalent) suffix results in garbled
+		// non-ASCII chars in translatated messages and also affects
+		// functions like mbrtowc() which depend on LC_CTYPE.
+		//
+		// Workaround the problem by not using libintl_setlocale()
+		// for now. Notes:
+		//
+		// (1) libintl_setlocale() reads LC_* environment variables
+		//     but native setlocale() doesn't. The loss of this
+		//     feature doesn't matter too much because, on Windows,
+		//     libintl still reads the env vars LANGUAGE, LC_ALL,
+		//     LC_MESSAGES, and LANG when translating messages in
+		//     the LC_MESSAGES category (other categories are very
+		//     rarely used for translations). As of Gettext commit
+		//     e18edc579 and Gnulib commit 9e301775ff:
+		//
+		//     libintl_gettext()
+		//      `-- libintl_dcgettext()
+		//           `-- libintl_dcigettext()
+		//                `-- guess_category_value()
+		//                     |-- gl_locale_name_posix()
+		//                     |    `-- gl_locale_name_posix_unsafe()
+		//                     |         `-- gl_locale_name_environ()
+		//                     |              |-- getenv("LC_ALL")
+		//                     |              |-- getenv("LC_MESSAGES")
+		//                     |              `-- getenv("LANG")
+		//                     `-- getenv("LANGUAGE")
+		//
+		// (2) If locale is changed, libintl_setlocale() marks cached
+		//     translations as invalid. bindtextdomain(), which we
+		//     call immediately after setlocale(), does the same
+		//     invalidation too. Thus it doesn't matter in the
+		//     tuklib_gettext_init() macro. It could matter if the
+		//     application calls setlocale() elsewhere though (but
+		//     then it's not guaranteed that such code even includes
+		//     <libint.h> in addition to <locale.h>).
+		//
+		// This macro is checked by <libintl.h> since Gettext 0.18.2
+		// (2012-12-08). When this is defined, setlocale() isn't
+		// overridden.
+		//
+		// FIXME: Remove this hack when it's no longer needed.
+#		define GNULIB_defined_setlocale 1
+#	endif
 #	include <libintl.h>
 #	define tuklib_gettext_init(package, localedir) \
 		do { \