That's inaccurate, according to the page you linked to (and to my memory of the incident). gcc 1.17 would invoke nethack (or one of several other similar games

That's inaccurate, according to the page you linked to (and to my memory of the incident). gcc 1.17 would invoke nethack (or one of several other similar games, if available) if it saw an unrecogized #pragma directive. According to the C standard, the behavior of a #pragma not followed by STDC is implementation-defined, not undefined -- which means that an implementation is required to document its behavior. (I presume that gcc did so.) gcc did not play launch Nethack in response to undefined behavior in general, or in response to anything other than an unrecognized #pragma directive.