fix ASSERT macros: return -1 instead of bare return in int main() (FreeBSD -Wreturn-mismatch)

tests/test_ll_queue.c

@@ -35,7 +35,7 @@ static struct {
 #define PASS()      do { puts("PASS"); stats.passed++; } while(0)
 #define FAIL(msg)   do { printf("FAIL: %s\n", msg); stats.failed++; } while(0)
 
-#define ASSERT(c, m) do { if (!(c)) { FAIL(m); return; } } while(0)
+#define ASSERT(c, m) do { if (!(c)) { FAIL(m); return -1; } } while(0)
 #define ASSERT_EQ(a,b,m) ASSERT((a)==(b),m)
 
 /* ------------------------------------------------------------------ */