Rollup merge of rust-lang#138993 - CAD97:cfg_match_semitransparent, r=dtolnay

Make `cfg_match!` a semitransparent macro

IIUC this is preferred when (potentially) stabilizing `macro` items, to avoid potentially utilizing def-site hygiene instead of mixed-site.

Tracking issue: rust-lang#115585

Author: matthiaskrgr

core/src/macros/mod.rs

@@ -237,9 +237,10 @@ pub macro assert_matches {
 /// ```
 #[unstable(feature = "cfg_match", issue = "115585")]
 #[rustc_diagnostic_item = "cfg_match"]
+#[rustc_macro_transparency = "semitransparent"]
 pub macro cfg_match {
     ({ $($tt:tt)* }) => {{
-        cfg_match! { $($tt)* }
+        $crate::cfg_match! { $($tt)* }
     }},
     (_ => { $($output:tt)* }) => {
         $($output)*
@@ -249,10 +250,10 @@ pub macro cfg_match {
         $($( $rest:tt )+)?
     ) => {
         #[cfg($cfg)]
-        cfg_match! { _ => $output }
+        $crate::cfg_match! { _ => $output }
         $(
             #[cfg(not($cfg))]
-            cfg_match! { $($rest)+ }
+            $crate::cfg_match! { $($rest)+ }
         )?
     },
 }