About pkg-config:
From http://www.freedesktop.org/wiki/Software/pkg-config
pkg-config is a helper tool used when compiling applications and
libraries. It helps you insert the correct compiler options on the
command line so an application can use gcc -o test test.c
`pkg-config --libs --cflags glib-2.0` for instance, rather than
hard-coding values on where to find glib (or other libraries). It is
language-agnostic, so it can be used for defining the location of
documentation tools, for instance.
pkg-config is a widely used build helper tool. Major build tools such
as GNU Autoconf, CMake and so on support pkg-config.
MessagePack users can build their software more easily.
