Fix build of sys crate when source directory is read-only

sys/Cargo.toml

@@ -14,3 +14,5 @@ links = "whisper"
 
 [build-dependencies]
 bindgen = "0.64"
+tempfile = "3.3.0"
+dircpy = "0.3.14"

sys/build.rs

@@ -57,8 +57,16 @@ fn main() {
         return;
     }
 
+    // copy sources to a temporary directory: in some build systems, the source repo can be read-only
+    // and the makefile compiles files in-place.
+    let temp_build_dir = tempfile::tempdir().expect("failed to acquire temporary directory");
+    dircpy::CopyBuilder::new("whisper.cpp", &temp_build_dir)
+        .with_exclude_filter(".git")
+        .run()
+        .expect("could not copy whisper.cpp to temporary directory");
+
     // build libwhisper.a
-    env::set_current_dir("whisper.cpp").expect("Unable to change directory");
+    env::set_current_dir(&temp_build_dir).expect("Unable to change directory");
     let code = std::process::Command::new("make")
         .arg("libwhisper.a")
         .status()