gist.h:

/*
** You can have as many strategies as you please in GiSTs, as
** long as your consistent method can handle them
*/
#define GISTNStrategies                 100
                                        ^^^
- too big number:

strat.h->StrategyEvaluationData->StrategyExpression  expression[12]
                                                                ^^
 - so 12 is real max # of strategies, or StrategyEvaluationIsValid
crashes backend (called if CASSER defined).