build: Link u-a against libintl if libc does not have i18n support

This happens on at least Solaris and Darwin.

Signed-off-by: Guillem Jover <guillem@debian.org>

debian/changelog

@@ -7,6 +7,10 @@ dpkg (1.15.8.4) UNRELEASED; urgency=low
   * On database parsing only warn on bogus versions previously accepted,
     the other instances will keep producing errors, to avoid newly
     introduced bogosity. Closes: #590885, #590896, #591692, #591885
+  * Fix compilation on Solaris and Darwin:
+    - Link update-alternatives against libintl if libc does not have i18n
+      support.
+    Thanks to Fabian Groffen <grobian@gentoo.org>.
 
   [ Raphaël Hertzog ]
   * Fix make -C man install so that it actually finds the manual pages

utils/Makefile.am

@@ -25,6 +25,7 @@ update_alternatives_SOURCES = \
 
 update_alternatives_LDADD = \
 	../lib/compat/libcompat.a \
+	$(LIBINTL) \
 	$(UA_LIBS)
 
 sbin_PROGRAMS =