swupdate: check if librsync is required

Signed-off-by: Pierre-Jean Texier <pjtexier@koncepto.io>
Acked-by: Stefano Babic <sbabic@denx.de>

recipes-support/swupdate/swupdate.inc

@@ -94,6 +94,10 @@ python () {
         depends = d.getVar('DEPENDS', False)
         d.setVar('DEPENDS', depends + ' libgpiod')
 
+    if 'CONFIG_RDIFFHANDLER=y\n' in features:
+        depends = d.getVar('DEPENDS', False)
+        d.setVar('DEPENDS', depends + ' librsync')
+
     if 'CONFIG_MONGOOSE_WEB_API_V2=y\n' in features:
         d.setVar('SWUPDATE_WWW', 'webapp')
 }