Rollup merge of #95802 - RalfJung:unused-win, r=Dylan-DPC

fix unused constant warning on some Windows targets

When none of those `cfg_if!` apply (and on Miri), the constant remains unused.

library/std/src/sys/windows/mod.rs

@@ -289,6 +289,7 @@ pub fn dur2timeout(dur: Duration) -> c::DWORD {
 /// that function for more information on `__fastfail`
 #[allow(unreachable_code)]
 pub fn abort_internal() -> ! {
+    #[allow(unused)]
     const FAST_FAIL_FATAL_APP_EXIT: usize = 7;
     #[cfg(not(miri))] // inline assembly does not work in Miri
     unsafe {