Don't check TIOCMGDTRWAIT or TIOCMSDTRWAIT on FreeBSD 15 (fails in CI)

Author: joshtriplett

libc-test/build.rs

@@ -2869,6 +2869,8 @@ fn test_freebsd(target: &str) {
             // Added in FreeBSD 14.2
             "SO_SPLICE" if Some(14) > freebsd_ver => true,
 
+            "TIOCMGDTRWAIT" | "TIOCMSDTRWAIT" if freebsd_ver >= Some(15) => true,
+
             _ => false,
         }
     });