Fix errors while building with clang

tools/db_sanity_test.cc

@@ -4,6 +4,7 @@
 //  of patent rights can be found in the PATENTS file in the same directory.
 
 #include <cstdio>
+#include <cstdlib>
 #include <vector>
 #include <memory>
 

util/arena.h

@@ -13,6 +13,7 @@
 
 #pragma once
 #include <cstddef>
+#include <cerrno>
 #include <vector>
 #include <assert.h>
 #include <stdint.h>

util/log_buffer.h

@@ -8,6 +8,7 @@
 #include "rocksdb/env.h"
 #include "util/arena.h"
 #include "util/autovector.h"
+#include <ctime>
 
 namespace rocksdb {