Fix breakage caused by CLOCK_BOOTTIME being removed from DragonFly.

rust-lang/libc#3509 removed `CLOCK_BOOTIME` from DragonFly, which broke
rustix.

Author: sunfishcode

src/backend/libc/time/syscalls.rs

@@ -167,7 +167,7 @@ pub(crate) fn clock_gettime_dynamic(id: DynamicClockId<'_>) -> io::Result<Timesp
         DynamicClockId::Tai => c::CLOCK_TAI,
 
         #[cfg(any(
-            freebsdlike,
+            target_os = "freebsd",
             linux_kernel,
             target_os = "fuchsia",
             target_os = "openbsd"