tracepointchecker.rb: needs TracePoint

* test/lib/tracepointchecker.rb: available only if TracePoint is
  available.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49097 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/lib/tracepointchecker.rb

@@ -109,10 +109,10 @@ module TracePointChecker
       raise "trace #{trace} should not be deactivated" unless trace.enabled?
     }
   end
-end
+end if defined?(TracePoint)
 
 class ::Test::Unit::TestCase
   include TracePointChecker::ZombieTraceHunter
-end
+end if defined?(TracePoint)
 
 # TracePointChecker.start verbose: false