Add missing stuff for custom plugins.

Change-Id: I34a35fe789d473b630b80c4f8f30833e0e04d188
Reviewed-on: https://code.wireshark.org/review/4981
Reviewed-by: Anders Broman <a.broman58@gmail.com>

CMakeLists.txt

@@ -922,6 +922,7 @@ set( IN_FILES
 	plugins/irda/plugin.rc.in
 	plugins/docsis/plugin.rc.in
 	plugins/easy_codec/plugin.rc.in
+	${CUSTOM_PLUGIN_IN_FILES}
 	ui/doxygen.cfg.in
 	ui/gtk/doxygen.cfg.in
 	ui/qt/doxygen.cfg.in

CMakeListsCustom.txt.example

@@ -26,3 +26,9 @@ set(CUSTOM_PLUGIN_SRC_DIR
 # or
 #   plugins/foo
 )
+
+set(CUSTOM_PLUGIN_IN_FILES
+#	private_plugins/foo/plugin.rc.in
+# or
+#   plugins/foo/plugin.rc.in
+)