pkg-config was probed up to three times per build: once inside
generate_bindings for the header include paths, once for linking, and
then main unconditionally emitted `cargo:rustc-link-lib=vlc` on top of the
directives the successful probe already prints, libvlc ended up on
the link line two or three times.
Probe a single time in main and thread the resulting Library into
generate_bindings for its include paths. Drop the manual rustc-link-lib
line, since a successful pkg_config probe emits it.
binding.rs generation with bindgen is optional.
By default, a pre-generated binding.rs is copied in OUT_DIR. This allows
for example to build on Windows and link against a standard VLC
installation.
Feature "use-bindgen" will trigger binding generation.
Alaric Senat