LD_PRELOAD by itself only works with Cygwin builtin functions, but
textdomain() and friends come from libintl.  In order to override
those functions, we have to "replace" cygintl-?.dll since functions are
bound to a DLL name at link time.  Our replacement will be used since
it is loaded first by LD_PRELOAD.

But as we are making this *the* libintl, we need to provide 
pass-throughs for the other functions which we're not overriding,
otherwise Locale::gettext won't load (not to mention the program
that we're trying to help2man).

--- help2man-1.46.5/Makefile.in	2014-10-09 13:03:01.000000000 +0200
+++ help2man-1.46.5/Makefile.in	2015-05-12 14:46:52.995521900 +0200
@@ -76,7 +76,8 @@
        fi

 install_preload: install_dirs preload
-	$(INSTALL_PROGRAM) $(preload).so $(DESTDIR)$(pkglibdir)
+	$(INSTALL_PROGRAM) lib/cygintl-8.dll $(DESTDIR)$(pkglibdir)
+	ln -sf cygintl-8.dll $(DESTDIR)$(pkglibdir)/$(preload).so

 install_l10n: install_dirs msg_l10n man_l10n info_l10n
        set -e; \
@@ -144,7 +146,9 @@

 preload: $(preload).so
 $(preload).so: $(srcdir)/$(preload).c
-	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -o $@ -fPIC -shared $? $(LIBS)
+	mkdir -p lib
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) -o lib/cygintl-8.dll -shared $? $(LIBS)
+	ln -sf lib/cygintl-8.dll $@

 man: $(target).1
 $(target).1: $(srcdir)/$(target).PL $(srcdir)/$(target).h2m.PL
--- help2man-1.46.5/bindtextdomain.c	2009-11-13 00:01:34.000000000 -0600
+++ help2man-1.46.5/bindtextdomain.c	2011-12-29 00:24:33.608078600 -0600
@@ -27,12 +27,34 @@ static char *(*r_textdomain)(char const
 static char *(*r_bindtextdomain)(char const *, char const *) = 0;
 static char *(*r_bind_textdomain_codeset)(char const *, char const *) = 0;
 
+#ifdef __CYGWIN__
+static void *RTLD_NEXT = 0;
+static char *(*r_gettext)(const char *) = 0;
+static char *(*r_dgettext)(const char *, const char *) = 0;
+static char *(*r_dcgettext)(const char *, const char *, int) = 0;
+static char *(*r_ngettext)(const char *, const char *, unsigned long int) = 0;
+static char *(*r_dngettext)(const char *, const char *, const char *,
+                            unsigned long int) = 0;
+static char *(*r_dcngettext)(const char *, const char *, const char *,
+                             unsigned long int, int) = 0;
+static char *(*r_setlocale)(int, const char *) = 0;
+
+#define SYM(sym) libintl_ ## sym
+#else
+#define SYM(sym) sym
+#endif
+
 void setup()
 {
     static int done = 0;
     if (done++)
         return;
 
+#ifdef __CYGWIN__
+    if (!(RTLD_NEXT = dlopen("/usr/bin/cygintl-8.dll", RTLD_LAZY)))
+        die("libintl8 not found");
+#endif
+
     if (!(e_textdomain = getenv("TEXTDOMAIN")))
 	die("TEXTDOMAIN not set");
 
@@ -48,9 +70,19 @@ void setup()
     if (!(r_bind_textdomain_codeset = dlsym(RTLD_NEXT,
     					    "bind_textdomain_codeset")))
 	die("can't find symbol \"bind_textdomain_codeset\"");
+
+#ifdef __CYGWIN__
+    r_gettext = dlsym(RTLD_NEXT, "libintl_gettext");
+    r_dgettext = dlsym(RTLD_NEXT, "libintl_dgettext");
+    r_dcgettext = dlsym(RTLD_NEXT, "libintl_dcgettext");
+    r_ngettext = dlsym(RTLD_NEXT, "libintl_ngettext");
+    r_dngettext = dlsym(RTLD_NEXT, "libintl_dngettext");
+    r_dcngettext = dlsym(RTLD_NEXT, "libintl_dcngettext");
+    r_setlocale = dlsym(RTLD_NEXT, "libintl_setlocale");
+#endif
 }
 
-char *textdomain(char const *domainname)
+char *SYM(textdomain)(char const *domainname)
 {
     char *r;
     setup();
@@ -61,7 +93,7 @@ char *textdomain(char const *domainname)
     return r;
 }
 
-char *bindtextdomain(char const *domainname, char const *dirname)
+char *SYM(bindtextdomain)(char const *domainname, char const *dirname)
 {
     char const *dir = dirname;
     setup();
@@ -71,7 +103,7 @@ char *bindtextdomain(char const *domainn
     return r_bindtextdomain(domainname, dir);
 }
 
-char *bind_textdomain_codeset(char const *domainname, char const *codeset)
+char *SYM(bind_textdomain_codeset)(char const *domainname, char const *codeset)
 {
     char *r;
     setup();
@@ -81,3 +113,54 @@ char *bind_textdomain_codeset(char const
 
     return r;
 }
+
+#ifdef __CYGWIN__
+
+char *libintl_gettext(const char *msgid)
+{
+    setup();
+    return r_gettext(msgid);
+}
+
+char *libintl_dgettext (const char *domainname, const char *msgid)
+{
+    setup();
+    return r_dgettext(domainname, msgid);
+}
+
+char *libintl_dcgettext (const char *domainname, const char *msgid,
+                         int category)
+{
+    setup();
+    return r_dcgettext (domainname, msgid, category);
+}
+
+char *libintl_ngettext (const char *msgid1, const char *msgid2,
+                        unsigned long int n)
+{
+    setup();
+    return r_ngettext (msgid1, msgid2, n);
+}
+
+char *libintl_dngettext (const char *domainname, const char *msgid1,
+                         const char *msgid2, unsigned long int n)
+{
+    setup();
+    return r_dngettext (domainname, msgid1, msgid2, n);
+}
+
+char *libintl_dcngettext (const char *domainname,
+                          const char *msgid1, const char *msgid2,
+                          unsigned long int n, int category)
+{
+    setup();
+    return r_dcngettext (domainname, msgid1, msgid2, n, category);
+}
+
+char *libintl_setlocale (int i, const char *s)
+{
+    setup();
+    return r_setlocale (i, s);
+}
+
+#endif