Summary:
Long absolute file names in log make it hard to read the LOG files.
So we shorter them to relative to the root of RocksDB project path.
In most cases, they will only have one level directory and one file name.
There was [a talk](#4316) about making "util/logging.h" a public header file.
But we concern the conflicts that might be introduced in for macros
named `STRINGIFY`, `TOSTRING`, and `PREPEND_FILE_LINE`.
So I prepend a prefix `ROCKS_LOG_` to them.
I also remove the line that includes "port.h" which seems unneccessary here.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4616
Differential Revision: D12892857
Pulled By: siying
fbshipit-source-id: af79aaf82153b8fd66b5966aced39a51fbca9c6c