Add ui test for unneeded_clippy_cfg_attr

Author: GuillaumeGomez

tests/ui/unnecessary_clippy_cfg.rs

@@ -0,0 +1,11 @@
+#![warn(clippy::unnecessary_clippy_cfg)]
+#![cfg_attr(clippy, deny(clippy::non_minimal_cfg))]
+#![cfg_attr(clippy, deny(dead_code, clippy::non_minimal_cfg))]
+#![cfg_attr(clippy, deny(dead_code, clippy::non_minimal_cfg, clippy::maybe_misused_cfg))]
+
+#[cfg_attr(clippy, deny(clippy::non_minimal_cfg))]
+#[cfg_attr(clippy, deny(dead_code, clippy::non_minimal_cfg))]
+#[cfg_attr(clippy, deny(dead_code, clippy::non_minimal_cfg, clippy::maybe_misused_cfg))]
+pub struct Bar;
+
+fn main() {}