Add tests for private items of cfg_accessible

Author: Urgau

src/test/ui/conditional-compilation/cfg_accessible-private.rs

@@ -0,0 +1,21 @@
+// check-pass
+
+#![feature(cfg_accessible)]
+
+mod private {
+    struct Struct;
+    enum Enum{}
+    union Union{_a:u8}
+}
+
+#[cfg_accessible(private::Struct)]
+const A: bool = true;
+
+#[cfg_accessible(private::Enum)]
+const A: bool = true;
+
+#[cfg_accessible(private::Union)]
+const A: bool = true;
+
+const A: bool = false; // Will conflict if any of those is accessible
+fn main() {}