rust: trace: libc does not have syslog on windows

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/trace/src/lib.rs

@@ -3,6 +3,7 @@
 //! This crate provides macros that aid in using QEMU's tracepoint
 //! functionality.
 
+#[cfg(not(windows))]
 #[doc(hidden)]
 /// Re-exported item to avoid adding libc as a dependency everywhere.
 pub use libc::{syslog, LOG_INFO};