(#1006): Do not probe system_deps when building for docs.rs, since it does not...
(#1006 (closed)): Do not probe system_deps when building for docs.rs, since it does not have the libraries we depend on
Basically, copy the magic from gtk4-rs. Use the "docsrs" feature to conditionally compile the part in build.rs that calls system_deps.
Fixes #1006 (closed)