Fix linking on Cygwin (bug #4561).

plugins/thunar-apr/Makefile.am

@@ -36,6 +36,7 @@ thunar_apr_la_CFLAGS =							\
 thunar_apr_la_LDFLAGS =							\
 	-avoid-version							\
 	-export-dynamic							\
+	-no-undefined							\
 	-export-symbols-regex "^thunar_extension_(shutdown|initialize|list_types)" \
 	-module								\
 	$(PLATFORM_LDFLAGS)

plugins/thunar-sbr/Makefile.am

@@ -41,6 +41,7 @@ thunar_sbr_la_CFLAGS =							\
 thunar_sbr_la_LDFLAGS =							\
 	-avoid-version							\
 	-export-dynamic							\
+	-no-undefined							\
 	-export-symbols-regex "^thunar_extension_(shutdown|initialize|list_types)" \
 	-module								\
 	$(PLATFORM_LDFLAGS)

plugins/thunar-uca/Makefile.am

@@ -39,6 +39,7 @@ thunar_uca_la_CFLAGS =							\
 thunar_uca_la_LDFLAGS =							\
 	-avoid-version							\
 	-export-dynamic							\
+	-no-undefined							\
 	-export-symbols-regex "^thunar_extension_(shutdown|initialize|list_types)" \
 	-module								\
 	$(PLATFORM_LDFLAGS)

plugins/thunar-wallpaper/Makefile.am

@@ -25,6 +25,7 @@ thunar_wallpaper_plugin_la_CFLAGS =					\
 thunar_wallpaper_plugin_la_LDFLAGS =					\
 	-avoid-version							\
 	-export-dynamic							\
+	-no-undefined							\
 	-export-symbols-regex "^thunar_extension_(shutdown|initialize|list_types)" \
 	-module								\
 	$(PLATFORM_LDFLAGS)

thunarx/Makefile.am

@@ -56,6 +56,7 @@ libthunarx_2_la_CFLAGS =						\
 libthunarx_2_la_LDFLAGS =						\
 	-export-dynamic							\
 	-export-symbols-regex "^[^_].*"					\
+	-no-undefined							\
 	-version-info $(THUNARX_VERINFO)				\
 	$(PLATFORM_LDFLAGS)