Do not run pretty tests by default.
diff --git a/src/bootstrap/check.rs b/src/bootstrap/check.rs
index ee58926..3e0cfa3 100644
--- a/src/bootstrap/check.rs
+++ b/src/bootstrap/check.rs
@@ -458,6 +458,9 @@
             });
         } else {
             for test in HOST_COMPILETESTS {
+                if test.mode == "pretty" {
+                    continue;
+                }
                 run.builder.ensure(HostCompiletest {
                     compiler,
                     target: run.target,