Add Xpress and ZSTD CompressionType values to C header
Add Xpress and ZSTD CompressionType values to C header

Summary:
This PR copies the missing CompressionType values
```cpp
enum CompressionType : unsigned char {
  ...
  kXpressCompression = 0x6,
  kZSTD = 0x7,
  ...
};
```
into the C header.
Closes https://github.com/facebook/rocksdb/pull/1989

Differential Revision: D4706265

Pulled By: siying

fbshipit-source-id: e65e62a

bbiao/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,Andymic/rocksdb,bbiao/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,vmx/rocksdb,Andymic/rocksdb,Andymic/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,Andymic/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,vmx/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,bbiao/rocksdb