Fixed incorrect const values

lib/mem/alloc_unix.q

@@ -0,0 +1,12 @@
+import sys
+
+alloc(length int) -> []byte {
+	x := sys.mmap(0, length+8, prot.read|prot.write, map.private|map.anonymous)
+
+	if x < 0x1000 {
+		return x
+	}
+
+	store(x, 8, length)
+	return x + 8
+}