Use rand() instead of random()

Use rand() instead of random() cause the latter is not available
on Windows and postgres stopped backporting it with PG15.
Ideally we switch to the crypto functions added in PG15 but that
requires a bit more work and this is the minimal change required
to get it to build against PG15 on Windows.

src/bgw/job_stat.c

@@ -272,7 +272,7 @@ static float8
 calculate_jitter_percent()
 {
 	/* returns a number in the range [-0.125, 0.125] */
-	uint8 percent = random();
+	uint8 percent = rand();
 	return ldexp((double) (16 - (int) (percent % 32)), -7);
 }
 
@@ -305,7 +305,7 @@ calculate_next_start_on_failure(TimestampTz finish_time, int consecutive_failure
 	MemoryContext oldctx;
 	/* 2^(consecutive_failures) - 1, at most 2^20 */
 	int64 max_slots = (INT64CONST(1) << (int64) multiplier) - INT64CONST(1);
-	int64 rand_backoff = random() % (max_slots * USECS_PER_SEC);
+	int64 rand_backoff = rand() % (max_slots * USECS_PER_SEC);
 
 	if (!IS_VALID_TIMESTAMP(finish_time))
 	{