build: Regenerate rpmostree-rust.h if cbindgen.toml changes

So when I edit it I get the changes.  Figuring this out
took me a little while, we were missing two dependencies.

Closes: #1559
Approved by: jlebon

Makefile-rpm-ostree.am

@@ -87,7 +87,7 @@ librpmostree_rust_path = @abs_top_builddir@/target/@RUST_TARGET_SUBDIR@/librpmos
 # want to (by default) touch the Internet during builds here.
 # One reason is that we want to support `make && sudo make install`,
 # and we don't want to do `sudo cargo` there.
-LIBRPMOSTREE_RUST_SRCS = $(wildcard rust/src/*.rs)
+LIBRPMOSTREE_RUST_SRCS = $(wildcard rust/src/*.rs) rust/cbindgen.toml
 $(librpmostree_rust_path): Makefile $(LIBRPMOSTREE_RUST_SRCS)
 	cd $(top_srcdir)/rust && \
 	  export CARGO_TARGET_DIR=@abs_top_builddir@/target && \

rust/build.rs

@@ -6,6 +6,10 @@ extern crate cbindgen;
 fn run() -> Result<(), String> {
     let out_dir_v = std::env::var("OUT_DIR").expect("OUT_DIR is unset");
     let out_dir = std::path::Path::new(&out_dir_v);
+
+    // First, output our dependencies https://doc.rust-lang.org/cargo/reference/build-scripts.html
+    println!("cargo:rerun-if-changed=cbindgen.toml");
+
     let bindings = cbindgen::generate(std::path::Path::new(".")).map_err(|e| e.to_string())?;
     // This uses unwraps internally; it'd be good to submit a patch
     // to add a Result-based API.