Rollup merge of rust-lang#134649 - SUPERCILEX:statx-remember, r=thomcc

Fix forgetting to save statx availability on success

Looks like we forgot to save the statx state on success which means the first failure (common when checking if a file exists) will always require spending an invalid statx to confirm the failure is real.

r? `@thomcc`

Author: jhpratt

library/std/src/sys/pal/unix/fs.rs

@@ -168,7 +168,8 @@ cfg_has_statx! {{
             ) -> c_int
         }
 
-        if STATX_SAVED_STATE.load(Ordering::Relaxed) == STATX_STATE::Unavailable as u8 {
+        let statx_availability = STATX_SAVED_STATE.load(Ordering::Relaxed);
+        if statx_availability == STATX_STATE::Unavailable as u8 {
             return None;
         }
 
@@ -200,6 +201,9 @@ cfg_has_statx! {{
                 return None;
             }
         }
+        if statx_availability == STATX_STATE::Unknown as u8 {
+            STATX_SAVED_STATE.store(STATX_STATE::Present as u8, Ordering::Relaxed);
+        }
 
         // We cannot fill `stat64` exhaustively because of private padding fields.
         let mut stat: stat64 = mem::zeroed();