lib: update_msgpack.sh: new script to update msgpack-c
lib: update_msgpack.sh: new script to update msgpack-c

To make easier maintenance of msgpack-c dependency, this patch introduce a
new script that downloads the latest msgpack-c from c_master branch and
makes a copy of the relevant source code.

It also generates a custom CMakeLists.txt file to build the library, this
has been done after finding many problems with the newest version build
system that got difficult to embed.

Signed-off-by: Eduardo Silva <81f705dc2ce1a61a2621e0e4b442a9474e1d0c70@treasure-data.com>

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