use CMAKE_CXX_STANDARD to set C++11 flags with CMake 3.1+ (apples flags are somehow different from standard clang)
port htonbe16/32/64 macros for rocksdb
use reinterpret_cast<size_t> to cast macOS's pthread_t (pointer type) to size_t , for rocksdb
This change add WITH_ROCKSDB_{LZ4,BZIP2,ZSTD,snappy} CMake variables
that can be set to ON/OFF/AUTO.
If variable has default value AUTO, rocksdb links with corresponding
compression library. OFF disables compiling/linking with specific compression
library, ON forces compiling with it (cmake would throw error if library
is not available)
Support for ZLIB is added unconditionally, as it is always there.
