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/panic_abort/src/lib.rs

@@ -65,6 +65,7 @@ pub unsafe extern "C-unwind" fn __rust_start_panic(_payload: *mut &mut dyn BoxMe
             //
             // Note: this is the same implementation as in libstd's `abort_internal`
             unsafe fn abort() -> ! {
+                #[allow(unused)]
                 const FAST_FAIL_FATAL_APP_EXIT: usize = 7;
                 cfg_if::cfg_if! {
                     if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {

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 {