Add support for reading and writing MessagePack, a binary object serialization format which aims to be more compact than text formats like JSON or YAML. The specification can be found at https://github.com/msgpack/msgpack/blob/master/spec.md
AMD is defining our next code object metadata format in terms of MessagePack, and the linked patches reflect that use.
This upsets ubsan
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/22688/steps/check-llvm%20ubsan/logs/stdio