tests: ignore some doctests on cross-compile

Author: jieyouxu

tests/run-make/doctests-merge/rmake.rs

@@ -1,3 +1,5 @@
+//@ ignore-cross-compile (needs to run doctests)
+
 use std::path::Path;
 
 use run_make_support::{cwd, diff, rustc, rustdoc};

tests/run-make/doctests-runtool/rmake.rs

@@ -1,5 +1,7 @@
 // Tests behavior of rustdoc `--runtool`.
 
+//@ ignore-cross-compile (attempts to run the doctests)
+
 use std::path::PathBuf;
 
 use run_make_support::rfs::{create_dir, remove_dir_all};