transform_mjit_header.rb: resurrect `exit false`

which was just unintentionally dropped at r62252.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62257 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/transform_mjit_header.rb

@@ -91,6 +91,7 @@ module MJITHeader
             STDERR.puts "possibly related lines:\n#{related_lines.join("\n")}"
           end
         end
+        exit false
       end
     end
   end