build: Make build copying more resilient

This fixes an issue where:

  1. User tries to build before initializing all submodules.
  2. `uplink-c` directory is empty and copied into build.
  3. Build fails but leaves empty `uplink-c` directory in build
     directory
  4. User initializes `uplink-c` and then tries to build again without
     cleaning.
  5. `uplink-c` gets nested in a second level deeper, causing build
     issues.

uplink-sys/build.rs

@@ -29,11 +29,18 @@ fn main() {
 
     // Directory containing uplink-c project for building
     let uplink_c_dir = out_dir.join("uplink-c");
-    // Copy project to OUT_DIR for building
+
+    // Make the output `uplink-c` directory if it doesn't exist.
+    Command::new("mkdir")
+        .args(["-p", &uplink_c_dir.to_string_lossy()])
+        .status()
+        .expect("Failed to create output uplink-c directory.");
+
+    // Copy the contents of the `uplink-c` project to the output `uplink-c` directory
     Command::new("cp")
         .args([
             "-R",
-            &uplink_c_src.to_string_lossy(),
+            &uplink_c_src.join(".").to_string_lossy(),
             &uplink_c_dir.to_string_lossy(),
         ])
         .status()