[feature request] allow linking to system libraries

[apteryks]

Hi,

The build currently relies on libraries bundled in source form under the src/thirdparty directory. It'd be nice if ccextractor's build system was able to detect compatible libraries from the system and use these instead, ideally being able to function even if the src/thirdparty directory does not exist.

freetype, libpng, utf8proc, zlib, protobuf-c at least are all available from my system for example (GNU Guix).

[cfsmp3]

We have vendored some libraries because it makes things much easier to build cross platform. Considering its size, it's just not worth the trouble of checking if there's a system version etc (and then dynamically link etc)

[apteryks]

@cfsmp3 CMake should make this relatively easy. It'd be a great improvement for distributions, as freetype and libpng have had security vulnerabilities in the past, so it's important to be able to patch these quickly (and updating/patching them in a single place is easier/faster for distros). I'll try to review PR #1761 now.