buildroot

msgpack: bump version to 2.1.5

Modern versions of msgpack are hosted on Github. Msgpack switched
their build systems from autotools to cmake a while back. The licence
was also updated from Apache to Boost.

Signed-off-by: bradford barr <bradford@density.io>
[Thomas: drop custom install commands, add LICENSE_1_0.txt to license
files.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>