build system fails to detect msgpack-c 6.0.0

[Apteryks]

Hi,

From version 4.0.0 onward, msgpack was split into msgpack-c and msgpack-cxx. The latest C package (msgpack-c) is at version 6.0.0 and ships a msgpack-c.pc pkg-config file.

Currently the build system fails to detect it:

checking for msgpack >= 1.1.0... no
configure: error: "msgpack >= 1.1.0 not found"

Thanks!