Update throw_unsup_format error message

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: tiif

src/shims/unix/linux/eventfd.rs

@@ -178,8 +178,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         }
         if flags != 0 {
             throw_unsup_format!(
-                "eventfd: Flags other than EFD_CLOEXEC, EFD_NONBLOCK \
-            and EFD_SEMAPHORE is not supported."
+                "eventfd: encountered unknown unsupported flags {:#x}"
             );
         }