mesa3d: util: rust: add proper stubs

Fixes some errors when compiling on non-traditional platforms.

Reviewed-by: David Gilhooley <djgilhooley.gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37097>

src/util/rust/sys/mod.rs

@@ -10,6 +10,9 @@ pub mod stub;
 #[cfg(windows)]
 pub mod windows;
 
+// Only Linux works for all cases.  Windows works for HANDLEs.
+// Tracking bug: https://gitlab.freedesktop.org/mesa/mesa/-/issues/13826
+
 cfg_if::cfg_if! {
     if #[cfg(any(target_os = "android", target_os = "linux"))] {
         pub use linux as platform;

src/util/rust/sys/stub/tube.rs

@@ -42,3 +42,9 @@ impl Listener {
         Err(MesaError::Unsupported)
     }
 }
+
+impl AsBorrowedDescriptor for Listener {
+    fn as_borrowed_descriptor(&self) -> &OwnedDescriptor {
+        unimplemented!()
+    }
+}

src/util/rust/sys/windows/tube.rs

@@ -42,3 +42,9 @@ impl Listener {
         Err(MesaError::Unsupported)
     }
 }
+
+impl AsBorrowedDescriptor for Listener {
+    fn as_borrowed_descriptor(&self) -> &OwnedDescriptor {
+        unimplemented!()
+    }
+}