Test #[allow(unused)] on if expression

Author: Aaron1011

src/test/ui/parser/if-attrs/builtin-if-attr.rs

@@ -0,0 +1,12 @@
+// check-pass
+
+fn main() {
+    #[allow(unused_variables)]
+    if true {
+        let a = 1;
+    } else if false {
+        let b = 1;
+    } else {
+        let c = 1;
+    }
+}