Fix some 32-bit compile errors

Summary: RocksDB doesn't compile on 32-bit architecture apparently. This is attempt to fix some of 32-bit errors. They are reported here: https://gist.github.com/paxos/8789697

Test Plan: RocksDB still compiles on 64-bit :)

Reviewers: kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15825

include/rocksdb/env.h

@@ -438,7 +438,7 @@ class WritableFile {
   // This asks the OS to initiate flushing the cached data to disk,
   // without waiting for completion.
   // Default implementation does nothing.
-  virtual Status RangeSync(off_t offset, off_t nbytes) {
+  virtual Status RangeSync(off64_t offset, off64_t nbytes) {
     return Status::OK();
   }