privat/nit — pull request #865 by privat (2014-11-01 18:16:30+00:00)
Title: tools: use pkg-config to found libgc

In some platform (mac?), the libgc library may not be located at standard default position.
Fortunately, libgc seems to be registered with pkg-config under most platforms.

Thus, use `pkg-config` in the generated makefiles to found the correct flags and paths.

In `c_src`, some generated files are manually modified to provide a working bootstrap under those platforms.

This is only a quick-and-dirty workaround. The real job must be polished and generalized to solve the issue #864