You can use Script Runner plugin – Edit: It unfortunately is no longer free. The last version before 4.0 still is, though. Details here https://www.adaptavist.com/doco/display/SFJ/Downgrade+ScriptRunner
It sports a ton of incredibly useful functions, one of these is hasLinks()
Usage example:
issueFunction in hasLinks("blocks") OR issueFunction in hasLinks("is blocked by")