Instructions for Updating LZ4 Version

This document describes the steps to update the bundled lz4 version, that is, the version used when ./configure is run with --disable-lz4-ext.

1. For each file in the lz4 repository's lib directory (checked out to the appropriate version tag), copy it into the librdkafka src directory, overwriting the previous files.
2. Copy xxhash.h and xxhash.c files, and rename them to rdxxhash.h and rdxxhash.c, respectively, replacing the previous files. Change any #includes of xxhash.h to rdxxhash.h.
3. Replace the #else block of the #if defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION) with the following code, including the comment:

    #else
    /* NOTE: While upgrading the lz4 version, replace the original `#else` block
    * in the code with this block, and retain this comment. */
    struct rdkafka_s;
    extern void *rd_kafka_mem_malloc(struct rdkafka_s *rk, size_t s);
    extern void *rd_kafka_mem_calloc(struct rdkafka_s *rk, size_t n, size_t s);
    extern void rd_kafka_mem_free(struct rdkafka_s *rk, void *p);
    # define ALLOC(s)          rd_kafka_mem_malloc(NULL, s)
    # define ALLOC_AND_ZERO(s) rd_kafka_mem_calloc(NULL, 1, s)
    # define FREEMEM(p)        rd_kafka_mem_free(NULL, p)
    #endif

4. Change version mentioned for lz4 in configure.self.
5. Run ./configure with --disable-lz4-ext option, make and run test 0017.
6. Update CHANGELOG.md and both the lz4 LICENSE, and the combined LICENSE.