apk: Use rustc --crate-type=cdylib to always force a lib to be comp…

…iled

This automatically turns `crate-type = ["*lib"]` and `[lib]` targets
into a `cdylib`, and otherwise errors appropriately when encountering a
binary instead of succeeding the build and having `cargo-apk` later
complain when `target/aarch64-linux-android/debug/lib<yourpacakge>.so`
is not found.

cargo-apk/src/apk.rs

@@ -226,7 +226,8 @@ impl<'a> ApkBuilder<'a> {
                 self.min_sdk_version(),
                 self.cmd.target_dir(),
             )?;
-            cargo.arg("build");
+            cargo.arg("rustc");
+            cargo.arg("--crate-type=cdylib");
             if self.cmd.target().is_none() {
                 cargo.arg("--target").arg(triple);
             }