Use compile_error! instead of use num_cpus

Author: hyd-dev

test-cargo-miri/subcrate/src/lib.rs

@@ -1,5 +1,5 @@
 #[cfg(doctest)]
-use num_cpus as _;
+compile_error!("rustdoc should not touch me");
 
 #[cfg(test)]
 compile_error!("Miri should not touch me");