Add test case for issue 6215

Author: ytmimi

tests/target/issue_6215.rs

@@ -0,0 +1,9 @@
+cfg_if!(
+    if #[cfg(feature = "xxxx")] {
+        if #[cfg(feature = "yyyy")] {
+            pub const C1: u8 = 1;
+        } else {
+            pub const C2: u8 = 2;
+        }
+    }
+);