Improve unexpected_cfgs lint when their is no value expected

compiler/rustc_lint_defs/src/lib.rs

@@ -426,7 +426,7 @@ pub enum BuiltinLintDiagnostics {
     BreakWithLabelAndLoop(Span),
     NamedAsmLabel(String),
     UnicodeTextFlow(Span, String),
-    UnexpectedCfg(Span, Symbol, Option<Symbol>),
+    UnexpectedCfg((Symbol, Span), Option<(Symbol, Span)>),
 }
 
 /// Lints that are buffered up early on in the `Session` before the