Commit
02b9b37698eb "Disable asserts in histogram code except in
--testing-mode" added a use of settings_get_testing_mode() but didn't
include the proper header. This fixes the problem.
#include <gsl/gsl_histogram.h>
#include <math.h>
#include <gsl/gsl_histogram.h>
#include <math.h>
+#include "data/settings.h"
#include "libpspp/message.h"
#include "libpspp/assertion.h"
#include "libpspp/cast.h"
#include "libpspp/message.h"
#include "libpspp/assertion.h"
#include "libpspp/cast.h"