This is a single .cpp file which can be added to your project to bring in LevelDB. It's easier than having to add all the individual sources to your Makefile or CMake or whatever. It also compiles much faster since its just one translation unit instead of many.

LevelDB Unity Source

// Set the appropriate LevelDB platform macro based on our platform.
//
#if BEAST_WIN32
 #define LEVELDB_PLATFORM_WINDOWS

#else
 #define LEVELDB_PLATFORM_POSIX

 #if BEAST_MAC || BEAST_IOS
  #define OS_MACOSX

 // VFALCO TODO Distinguish between BEAST_BSD and BEAST_FREEBSD
 #elif BEAST_BSD
  #define OS_FREEBSD

 #endif

#endif

#if BEAST_MSVC
#pragma warning (push)
#pragma warning (disable: 4018) // signed/unsigned mismatch
#pragma warning (disable: 4244) // conversion, possible loss of data
#endif

#include "leveldb/db/builder.cc"
#include "leveldb/db/db_impl.cc"
#include "leveldb/db/db_iter.cc"
#include "leveldb/db/dbformat.cc"
#include "leveldb/db/filename.cc"
#include "leveldb/db/log_reader.cc"
#include "leveldb/db/log_writer.cc"
#include "leveldb/db/memtable.cc"
#include "leveldb/db/repair.cc"
#include "leveldb/db/table_cache.cc"
#include "leveldb/db/version_edit.cc"
#include "leveldb/db/version_set.cc"
#include "leveldb/db/write_batch.cc"

#include "leveldb/table/block.cc"
#include "leveldb/table/block_builder.cc"
#include "leveldb/table/filter_block.cc"
#include "leveldb/table/format.cc"
#include "leveldb/table/iterator.cc"
#include "leveldb/table/merger.cc"
#include "leveldb/table/table.cc"
#include "leveldb/table/table_builder.cc"
#include "leveldb/table/two_level_iterator.cc"

#include "leveldb/util/arena.cc"
#include "leveldb/util/bloom.cc"
#include "leveldb/util/cache.cc"
#include "leveldb/util/coding.cc"
#include "leveldb/util/comparator.cc"
#include "leveldb/util/crc32c.cc"
#include "leveldb/util/env.cc"
#include "leveldb/util/filter_policy.cc"
#include "leveldb/util/hash.cc"
#include "leveldb/util/histogram.cc"
#include "leveldb/util/logging.cc"
#include "leveldb/util/options.cc"
#include "leveldb/util/status.cc"

// Platform Specific

#if defined (LEVELDB_PLATFORM_WINDOWS)
# include "leveldb/util/env_win.cc"
# include "leveldb/port/port_win.cc"

#elif defined (LEVELDB_PLATFORM_POSIX)
# include "leveldb/util/env_posix.cc"
# include "leveldb/port/port_posix.cc"

#elif defined (LEVELDB_PLATFORM_ANDROID)
# error Missing Android port!

#endif

#ifdef BEAST_MSVC
#pragma warning (pop)
#endif