Use new public libtest ERROR_EXIT_CODE constant in rustdoc

Author: GuillaumeGomez

src/librustdoc/doctest.rs

@@ -409,9 +409,7 @@ pub(crate) fn run_tests(
         // We ensure temp dir destructor is called.
         std::mem::drop(temp_dir);
         times.display_times();
-        // FIXME(GuillaumeGomez): Uncomment the next line once #144297 has been merged.
-        // std::process::exit(test::ERROR_EXIT_CODE);
-        std::process::exit(101);
+        std::process::exit(test::ERROR_EXIT_CODE);
     }
 }