clar: check for failing calloc() calls

We're not consistently checking for failing calls to `calloc()`. Do so
and adapt all callsites to use `clar_abort()`.

clar.c

@@ -383,7 +383,8 @@ clar_run_suite(const struct clar_suite *suite, const char *filter)
 
 		_clar.active_test = test[i].name;
 
-		report = calloc(1, sizeof(struct clar_report));
+		if ((report = calloc(1, sizeof(*report))) == NULL)
+			clar_abort("Failed to allocate report.\n");
 		report->suite = _clar.active_suite;
 		report->test = _clar.active_test;
 		report->test_number = _clar.tests_ran;
@@ -476,9 +477,10 @@ clar_parse_args(int argc, char **argv)
 
 					switch (action) {
 					case 's': {
-						struct clar_explicit *explicit =
-							calloc(1, sizeof(struct clar_explicit));
-						assert(explicit);
+						struct clar_explicit *explicit;
+
+						if ((explicit = calloc(1, sizeof(*explicit))) == NULL)
+							clar_abort("Failed to allocate explicit test.\n");
 
 						explicit->suite_idx = j;
 						explicit->filter = argument;
@@ -661,7 +663,10 @@ void clar__fail(
 	const char *description,
 	int should_abort)
 {
-	struct clar_error *error = calloc(1, sizeof(struct clar_error));
+	struct clar_error *error;
+
+	if ((error = calloc(1, sizeof(*error))) == NULL)
+		clar_abort("Failed to allocate error.\n");
 
 	if (_clar.last_report->errors == NULL)
 		_clar.last_report->errors = error;