Move raw FFI bindings generation to separate crates. This makes it
possible to reuse bindgen declarations for a header file in its
dependencies (this was not the case before this change), while keeping
multiple -sys crates to avoid rebuilding all the code whenever
something changes.
Because the -sys crates are generated in dependency order, this also
enforces that the crates are organized in something that resembles
the dependencies between C headers.
The meson.build for rust-safe crates becomes simpler, and it should be
possible in the future to let Meson's cargo support handle most of it.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[General cleanup and Python script. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
