build: Explicitly link to libdl

https://bugzilla.gnome.org/show_bug.cgi?id=794281

configure.ac

@@ -120,6 +120,13 @@ PKG_CHECK_MODULES([GTK],[
   freetype2
 ])
 
+sv_LIBS="$LIBS"
+LIBS=
+AC_SEARCH_LIBS([dlsym],[dl])
+LIBDL="$LIBS"
+LIBS="$sv_LIBS"
+AC_SUBST([LIBDL])
+
 GLIB_GENMARSHAL="$($PKG_CONFIG --variable=glib_genmarshal glib-2.0)"
 AC_SUBST([GLIB_GENMARSHAL])
 GLIB_MKENUMS="$($PKG_CONFIG --variable=glib_mkenums glib-2.0)"

gucharmap/Makefile.am

@@ -156,6 +156,7 @@ gucharmap_LDFLAGS = \
 gucharmap_LDADD = \
 	libgucharmap@GUCHARMAP_LIBRARY_SUFFIX_U@.la	\
 	$(GTK_LIBS)	\
+	$(LIBDL) \
 	$(INTL_LIBS)
 
 dist_noinst_DATA = gucharmap-menus.ui