Summary:
This change updates PosixSequentialFile::Read to call clearerr()
before fread()ing again after an EINTR is returned on a previous
fread.

The original fix is from https://github.com/cockroachdb/rocksdb/commit/bd8f1ebb91bbf0e668d24faef273042cc1fe52de.
Fixing https://github.com/facebook/rocksdb/issues/6509Signed-off-by: Nphantomape <cxucheng@outlook.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6609

Reviewed By: zhichao-cao

Differential Revision: D20731482

Pulled By: riversand963

fbshipit-source-id: 7f1f3a1449077d5560f45c465a78d08633740ba0