fixing issue #976

fixed https://github.com/kframework/k/issues/976

@dwightguth please review
if you don't want to do this now, it's not necessary, but I should point out that BuiltinVisitorOperations is constructed by Guice, so if you want to bind a boolean value in the configuration, you can pass it to the constructor of this class and it will automatically propagate from the part of the code that knows whether you have passed the --pattern-matching flag.